Talk:Journal of Comparative Neurology 22 (1912)
THE JOURNAL
OF
COMPARATIVE NEUROLOGY
EDITORIAL BOARD Henry H. Donaldson Adolf Meyer
The Wlstar Institute Johns Hopkins University
J. B. Johnston Oliver S. Strong
University of Minnesota Columbia University
C. JUDSON HerricK, University of Chicago Managing Editor
VOLUME 22
1912
PHILADELPHIA, PA. THE WISTAR INSTITUTE OF ANATOMY AND BIOLOGY
in
COMPOSED AND PRINTED AT TH2
WAVERLY PRESS
By the Williams & Wii.kins Compant
Baltimore, U. S. A.
CONTENTS
1912
No. 1. FEBRUARY
F. L. Landacre. The epibranchial placodes of Lepidosteus osseus and their relation to the cerebral ganglia. Fifty-eight figures 1
Henry H. Donaldson. A comparison of the European Norway and albino rats (Mus norvegicus and Mus norvegicus albinus) with those of North America with respect to the weight of the central nervous system and to cranial capacity. Five figures 71
No. 2. APRIL
Henry 0. Feiss. Experimental studies of paralyses in dogs after mechanical lesions in their spinal cords with a note on 'fusion' attempted in the Cauda equinas or the sciatic nerves. Twenty-seven figures 99
Elizabeth Hopkins Dunn. The influence of age, sex, weight and relationship upon the number of medullated nerve fibers and on the size of the largest fibers in the ventral root of the second cervical nerve of the albino rat. Six figures 131
S. Walter Ranson. The structure of the spinal ganglia and of the spinal nerves. Fifteen figures 159
No. 3. JUNE
Ralph Edward Sheldon. The olfactory tracts and centers in teleosts.
Forty-two plates 177
No. 4. AUGUST
J. B. Johnston. The telencephalon in cyclostomes. Forty-one figures.... 341
iii
IV CONTENTS
No. 5. OCTOBER
Samuel C. Palmer. The numerical relations of the histological elements in the retina of Necturus maculosus (Raf.). Twelve figures 405
F. W. Carpenter. On the histology of the cranial autonomic ganglia of the sheep. Ten figures 447
F. L. Landacre and Marie McLellan. The cerebral ganglia of the embryo of Rana pipiens. Eleven figures 461
No. 6. DECEMBER
S. Walter Ranson. Degeneration and regeneration of nerve fibers.
Twenty-nine figures 487
Ezra Allen. The cessation of mitosis in the central nervous system of the albino rat. Twenty-two figures 547
THE EPIBRANCHIAL PLACODES OF LEPIDOSTEUS
OSSEUS AND THEIR RELATION TO THE
CEREBRAL GANGLIA
F. L. LANDACRE
From the Department of Zoology, Ohio State University
FIFTY-EIGHT FIGURES
CONTEXTS
Introduction 1
Material 4
The 10 mm. embryo (general) 6
The ganglia and nerves of the 10 mm. embryo 8
The profundus ganglion 9
The Gasserian ganglion 10
The dorso-lateral VII 12
The geniculate ganglion 13
The ventro-lateral VII 14
The auditory ganglion 16
The glossopharyngeus ganglion 16
The vagus ganglia 17
The lateralis X 18
The branchial ganglia of X 18
Detailed description of the epibranchial placode of VII 19
The later history of the epibranchial placode of VII 22
The origin of the epibranchial placode of VII 23
Summary of the history of the first epibranchial placode 30
The epibranchial placode of the IX nerve 32
The first epibranchial placode of the X 36
The second epibranchial placode of the X 38
The third and fourth epibranchial placodes of the X 38
General summary and discussion 39
Literature cited 48
INTRODUCTION
A description of the origin and fate of the epibranchial placodes of Lepidosteus was undertaken with the object of extending our knowledge of the part these placodes play in the formation of the cerebral ganglia. Ectodermic thickenings, in the
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 1 FEBRUARY, 1912
1
2 F. L. LANDACRE
region of the gill slits, concerned in the formation of the cerebral ganglia, have been known for a long time through the work of Beard ('85), Van Wijhe ('82), Froriep ('85) and others and seem to be present in all classes of vertebrates including the higher mammals.
The mode of origin of the placodes in many forms is such that it is difficult to determine whether there is an actual contribution of cells by the placode to the corresponding ganglion. In most types described, the neural crest which enters into the composition of a given ganglion such as the VII, IX and X, comes into contact at its ventral border with the epidermis just dorsal and posterior to the corresponding gill pocket, and it is difficult to determine just how far the contact is due to the lateral extension of the neural crest portion of the ganglion as contrasted with the mesial ingrowth of the cell mass derived from the thickening of the ectoderm or placode.
In some types such as the catfishes (Landacre, '10), however, the mode of origin of the epibranchial placodes is such that the conditions are easy to interpret. The epibranchial placodes of the VII, IX and first two branchial ganglia of the X arise free from contact with the endodermic gill pockets and become detached from the epidermis en masse and are added to the remaining portions of the cerebral ganglia in such a manner that they can be followed with ease up to the time they become fused with the neural crest ganglia. The last two branchial ganglia of the X do not appear until the neural crest gangha in their downward growth approach the skin, and consequently do not furnish such good evidence of the integrity and continuity of their placodes. All these cell masses derived from the placodes, except in the case of the IX, become indistinguishably fused with the general visceral ganglia derived from the neural crest or its homologue in the lateral mass.
The condition of the epibranchial placode in the IX ganglion of Ameiurus is of the greatest importance in determining the significance of these structures. The visceral portion of this gangHori seems to come exclusively from the epibranchial placode
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS S
of the first true gill and the visceral portion of the ganglion is detached from the lateralis portion. Herrick ('07) found only special visceral or gustatory fibers arising from the visceral ganglion so that, since the visceral portion of the ganglion is exclusively placodal in origin, we are warranted in concluding that the epibranchial placodes give rise to those ganglionic cells from which gustatory fibers arise. This conclusion is strengthened by a number of facts that need not be repeated here. It does not seem an unwarranted conclusion that this is the function of the epibranchial placodes in all classes of vertebrates, although its demonstration in the higher vertebrates will always be a differcult undertaking, owing to the fact that the relations of the placode to the general visceral ganglion rarely seem to be so diagrammatic as in Ameiurus and that it is extemely difficult to secure a series of embryos of the higher vertebrates in stages sufficiently close to follow all the changes, since these series must in the lower forms, at least, be as close as four hours.
These facts emphasize the necessity of clearing the problem up as far as possible among the lower vertebrates, where series can be secured at sufficiently close intervals and where we should expect to find simpler relations owing to the generalized conditions of the peripheral nervous system. Of equal importance with the two facts just mentioned, however, is that of the hypertrophy of some of the components of the peripheral nerves, especially among the Ichthyopsida. This is probably the reason for the diagrammatic simplicity of the special visceral system of Ameiurus.
While Lepidosteus was taken up primarily because it is a generalized type, it appears that there is a beautiful example of hypertrophy in the case of the visceral portion of the VII ganglion as compared with the same ganglia in the IX and X. This is probably associated with the elongation of the head and the consequent increase in the area supplied by the VII nerve.
One of the principal difficulties encountered in the study of the placodes in Lepidosteus arises from the fact that the endodermal evagination from the pharynx is long anterio-posteriorly,
4 F. L, LANDACRE
and seems to encroach upon the territory occupied by the ectodermic evagination forming the placode; at least the placode is so closely applied to the posterior surface of the pharyngeal pocket that it is often difficult and sometimes impossible to tell where one ends and the other begins. Aside from this feature the conditions are quite similar to those found in Ameiurus with the exception that the visceral portion of the IX is not purely placodal in origin and that the placode of the VII nerve is much larger in Lepidosteus than in Ameiurus. In view of these facts I shall describe the placode of the VII nerve in detail, and treat the remaining placodes briefly.
MATERIAL
The material consists of thirty-three stages taken at intervals of six hours from one lot of eggs. Usually this would be too long an interval to follow accurately the changes in the cerebral ganglia but, by cutting a large number of series of any given age, it is rare that one cannot pick out some one of a given series that is as far advanced or even further advanced than the youngest stage of the next older series; so that if the series are sufficiently numerous they become practically continuous. The sections were cut 6 fx thick and stained in bulk in Delafield's haematoxylin one-sixth the strength of the stock solution, for twenty-four hours. This gave a much better differentiated stain than when sections were stained on the slide and owing to the amount of yolk granules present is much superior to Heidenhain's stain.
Table 1 shows the age, length and increments in age and length of embryos of Lepidosteus osseus ranging from 100 hours after fertilization to 272 hours after fertilization. Several series younger than 100 hours are referred to in the body of the paper but are not included in the table because they had not been freed from the membranes before fixation and consequently could not be measured accurately. They are referred to by age only.
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS
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F. L. LANDACRE
THE 10 MM. EMBRYO (GENERAL)
Owing to the fact that the nerve components of the adult Lepidosteus have not been worked and that there are some pecuharities in the size and arrangement of the gangha and nerves, it will simplify the description of the placodes to give a general account of structures and to give a rather complete account of the ganglia and nerves of some stage, for which I have selected the 10 mm. embryo.
This stage represents an intermediate condition in the formation of the epibranchial ganglia; the placodes being completely detached from the epidermis in the geniculate or VII ganglion, in process of formation in the IX or petrosal and first two epibranchial ganglia of the X, while the two remaining epibranchial placodes of the X are not yet present, there being only three well defined gill bars.
The general form of the anterior end of the body is quite characteristic as shown in fig. 1. The anterior end of the head has a sharp downward flexure beginning in the region of the infundibulum and ends in a prominent sucking disc. Directly over the posterior end of the infundibulum lies the mesencephalon which marks the highest point on the dorsal surface of the body.
The mouth is open and the pharynx has a cavity to a point just posterior to the third gill. Neither teeth not taste buds can be detected in the oral cavity or pharynx.
No cartilages are present at this stage, although the primordia of both cartilaginous and muscular structures can be identified in condensed masses of mesoderm.
The olfactory capsule has no cavity and is attached to the ectoderm throughout almost its whole length. Both roots of the olfactory nerve are well formed, that is, fibrillated and there are a number of loose cells lying around the nerve that probably develop later into the ganglion of the nervus terminalis. The optic vesicle is large, and elongated slightly in its anterior-posterior axis.
The auditory vesicle is a simple sac slightly elongated from anterior to posterior and has a short ductus endolymphaticus.
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 7
The supra-orbital, sub-orbital, mandibular and body sensory lines are present (figs. 6, 7, 15) and well defined and the position of some of the lateral line organs can be determined, although they are not well differentiated and not all of them are present, even on the head. The epidermal thickenings (figs. 8 and 9) forming the caudal extension of the epibranchial placodes are present and extend from the point of origin of the epibranchial placodes of the VII and IX nerves. They can be distinguished histologically from the primordia of the lateral lines in both the VII and IX nerves, and in the case of the IX, lie at a lower level than the primordia of the lateral lines.
The brain (fig. 1) at this stage shows a few of the peculiarities that are so pronounced in the adult Lepidosteus. The three primitive brain vesicles are still present. The telencephalon is not sharply separated dorsally from the diencephalon ; in fact, except for arbitrary landmarks it is not possible to define the two divisions of the primitive prosencephalon. The epiphysis and dorsal sac are present at the boundary between the thin walled prosencephalon and thick walled mesencephalon, but the paraphysis is not present and appears first in an embryo of 11 5 mm. as a definite evagination, although its position can be determined somewhat earlier as a thickened area in the roof of the prosencephalon. With the appearance of the paraphysis comes the elevation and broadening of the thin roof of the telencephalon which marks it off as distinct from the diencephalon.
Ventrally the hypophysis is well developed and there is a marked flexure in the floor of the brain directly under the mesencephalon and directly over a point just anterior to the posterior end of the hypophysis. The pituitary body is well developed at this stage. The mesencephalon is well developed and rises considerably above the level of the roof of the brain and consists of a large flattened vesicle which extends laterally over the anterior end of the metencephalon and has uniformly thick walls (figs. 6 and 7). These lateral lobes of the mesencephalon completely conceal the anterior end of the metencephalon from the dorsal surface. The roof of the brain is of uniform thickness from the region of the epiphysis to the posterior end of the mesencephalon.
8 F. L. LANDACRE
The anterior end of the metencephalon (figs. 6 and 7) consists of two lateral lobes with thick dorsal and ventral walls but with thin lateral walls. These, as mentioned above, are overhung by the broad flat mesencephalon. The anterior ends of these lobes are almost in contact with the posterior ends of the optic vesicles (fig. 1). At a point dorsal to the posterior end of the hypophysis they fuse on the median line and at a level with the entrance of the root of the Gasserian ganglion their cavities become confluent with the median ventricle. The roof of these vesicles is thick from their anterior end to a point just posterior to the posterior end of the mesencephalon. These two thick walled vesicles I take to be the lateral lobes of the cerebellum and the thickened roof of the anterior end of the metencephalon, lying under the posterior end of the mesencephalon and above the unpaired ventricle of the brain, the middle lobe of the cerebellum (valvula cerebeUi) . From the posterior end of the mesencephalon the roof of the metencephalon has the usual character of the medulla.
THE GANGLIA AND NERVES OF THE 10 MM. EMBRYO
Since the components of the cranial nerves in the adult Lepidosteus have not been worked out, certain difficulties present themselves when one attempts to identify the ganglia and nerves of the 10 mm. embryo. Some of these difficulties will appear in the description. For the most part, however, the identification of ganglia and nerves and even the identification of the components can be made with ease, owing to the isolated position of the ganglia and the solitary course pursued by components which are later combined into mixed nerve trunks. In the main, the position of definite ganglia is remarkably constant among the Ichthyopsida. The most striking differences among ganglia are three: (1) the presence or absence of the profundus ganglion; (2) the position of the ventro-lateral laterahs of the VII; and (3) the extent to which the branchial ganglia of the vagus are distinct. The profundus is present in Lepidosteus.
THE EPIBRANCHIAL GANGLIA OP LEPIDOSTEUS 9
The ventro-lateral lat. is mesial to the geniculate, while it is lateral in the Amphibia (Coghill, '02); and lastly the branchial ganglia of the X, in contrast with the Amphibia, are fairly distinct.
The branchial ganglia of the 10 mm. embryo are in an intermediate stage, as stated above, the branchial ganglion of the VII being completely formed, or rather detached from the epidermis, and the last two branchial ganglia of the X not yet formed owing to the absence of the last two gills. The same statement can be made of the ganglia as a whole. The V, VII, VIII and IX ganglia are definitely outlined, while the posterior portion of the X, the visceral portion, is not definitely formed.
The general visceral and general somatic ganglia which arise from the neural crest pass through a stage when their cells are quite loosely arranged and their boundaries are indefinite, so that, during the early stages in the formation of neural crest ganglia it is difficult to determine the exact limits of their boundaries. The general visceral X is in this condition in the 10 mm. embryo. If one chooses an older embryo, however, in which the X ganglia are fully formed, the V and VII ganglia are fused to such an extent that it renders their description difficult unless the nerve components are readily separable by differences in size. This condition is not reached in a 6-inch Lepidosteus. The process of fusing of ganglia is particularly true in the case of the lateraUs VII and the auditory. There is usually a brief period during the growth of these ganglia when their boundaries can be made out; but preceding and following this period the general visceral VII, lateralis VII, and auditory are likely to be more or less fused.
The profundus ganglion {ganglion mesencephali; trigeminus I)
This ganglion lies dorsal to the posterior portion of the optic vesicle (figs. 1, 4, 5). It is an elongated cord-like mass of cells placed diagonally in the mesoderm between the posterior portion of the optic vesicle and the mesencephalon. The anterior end
10 F. L. LANDACRE
extends dorsal to the upper border of the vesicle and the posterior end lies at a lower level. The nerve trunk (ophthalmicus profundus) which arises at the anterior end of the ganglion can be followed forward at this stage to a point over the anterior end of the lens where it becomes so attenuated that it cannot be followed further.
The nerve forms a gentle curve corresponding to the dorsal surface of the optic vesicle and maintains a constant position over the middle of the optic vesicle. The ophthalmicus profundus does not at this stage come into contact with either the ophthalmicus superficialis VII or the ophthalmicus superficialis V and is presumably a pure general somatic nerve, although in the early stages of the formation of the ganglion (82 hours) there is a pronounced contact with the epidermis, but whether this is placodal in nature or not has not been determined. The root of the profundus arises from the posterior end of the ganglion and passes back and down arching under the lateral lobes of the metencephalon which it enters from the ventral surface. The root forms a gentle curve down and back reversing the relations of the trunk. At the middle of its course the root comes into intimate relations with the third nerve, and somewhat further posterior, with the ciliary ganglion also.
The Gasserian ganglion {trigeminus II)
This ganglion (fig. 1) in the 10 mm. embryo is a large oblong ganglion placed diagonally in the mesoderm with its anterior end at the side of the oral cavity and above the level of the roof of the oral cavity. It is nowhere in contact with the epidermis. It extends from a point just anterior to the pituitary body, where it is located under the posterior portion of the optic vesicle, back to a point at the level of the anterior end of the dorso-lateral portion of the lateralis VII ganghon. It is not in contact with either the profundus (trigeminus I), or the geniculate ganglion of the VII, nor with the dorso-lateral VII. The ganglion is compact and definitely outlined. Its root is at the posterior end and is quite short, the ganglion cells at this point being closely attached
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 11
to the ventro-lateral wall of the medulla at a point opposite the posterior end of the mesencephalic roof.
There are two well defined fibrillated nerves arising from this ganglion at this time, a supra-orbital trunk (ophthalmicus superficialis trigeminus), and an infra-orbital trunk (truncus infraorbitalis), which splits up into the maxillary and mandibular trunks.
The supra-orbital trunk (fig. 1) arises from the dorsal surface of the posterior end of the ganglion and runs upward and slightly forward and becomes so attenuated that it cannot be followed as far forward as the posterior border of the optic vesicle. There is consequently no connection between supra-orbital V and the profundus, such as we see later when these two nerve trunks come to lie closer together.
The infra-orbital trunk is much larger and longer. It arises from the extreme anterior and ventral end of the ganglion. It is separated from the point of origin of the supra-orbital trunk by the whole length of the ganglion. This condition is of course temporary, since the Gasserian ganglion becomes shorter as it becomes older, and the two points of origin are brought closer together. Near its point of origin the infra-orbital trunk divides into two branches, a dorsal, the ramus maxillaris V (figs. 4 and 5) and a ventral, the ramus mandibularis V. The ramus maxillaris pursues a course forward under the optic vesicle at the level of its point of origin and can be followed to the anterior border of the vesicle. The ramus mandibularis V runs directly ventral into the mandible. All the nerves arising from the Gasserian ganglion, owing to their freedom from contact with other nerves and ganglia, are at this time pure general somatic nerves.
The VII ganglion is composed, as usual among Ichthyopsida, of three more or less distinct masses; a visceral ganglion, the geniculate, and two lateralis ganglia, the dorso-lateral and ventrolateral. There is more or less fusion between these ganglionic masses as well as with the auditory ganglion at various stages of their growth and migration into the adult condition; so that it will be easier to describe them in the order of their simplicity.
12 F. L. LANDACRE
The dorso-lateral VII
This ganglion (figs. 1, 8, 9) is an elongated rod-like mass occupying a position at the side of the anterior end of the medulla on a level with the floor of the medulla and between it and the epidermis. Its anterior end reaches as far forward as the root of the Gasserian, being situated of course more laterally, and its posterior end reaches posterior to the anterior end of the auditory vesicle and lies between the auditory vesicle and the medulla. The anterior end of the ganglion lies near the skin, while the posterior end lies near the cord, so that on a frontal section, it has a position diagonal to the longitudinal axis of the body. Its root enters the medulla along with the roots of the geniculate and ventro-lateral ganglion. It maintains about the same level dorso-ventrally throughout its course lying parallel with the long axis of the body. The posterior end of the ganglion comes into close contact with the posterior end of the geniculate and the anterior end of the auditory, the root fibers passing dorsally from the cells along the anterior end of the auditory ganglion.
There are three fibrillated nerves arising from this ganglion at this stage; a supra-orbital ramus, an infra-orbital ramus, and the ran^us oticus. The first two arise from the anterior end of the ganglion and shortly beyond their origin from the ganglion come closely into contact with the skin, where they innervate lateral line organs anterior to the position of the ganghon. Neither of these rami comes into close relation with the corresponding rami of the Gasserian, so that we do not have true supra-orbital and infra-orbital trunks at this time. The supraorbital ramus (laterahs portion of ramus ophthalmicus superficialis VII, figs. 4 to 7) arises from the dorsal portion of the anterior end of the ganglion, pursues a course diagonally forward and upward innervating lateral line organs of the supra-orbital line. It arches over the optic vesicle and can be traced with certainty as a fibrillated root to the anterior end of the optic vesicle. It always occupies a position quite close to the epidermis.
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 13
The infra-orbital ramus, ramus buccalis (figs. 4 to 7), originates from the ventral portion of the anterior end of the ganglion and pursues a course downward and forward in close contact with the skin where it can be followed as a fibrillated cord to a point near the anterior end of the optic vesicle. It innervates lateral line organs of the infra-orbital line anterior to the position of the ganglion. The ramus oticus is represented by a small twig arising midway between the anterior and posterior ends of the ganglion. It supplies the last lateral line organ in the infra-orbital line. The twig runs laterally from the ganglion and passes under the anterior end of the auditory capsule and can be followed easily throughout its whole course at this stage.
The geniculate ganglion
The geniculate ganglion is an elongated mass of cells placed diagonally in the body with the anterior end situated somewhat more ventrally and lying directly on the dorsal surface of the pharyngeal pocket (figs. 1 and 8). The anterior end of the ganglion lies as far forward as the posterior end of the Gasserian. The posterior end of the ganglion rises to the level of the base of the medulla and its root enters the medulla along with those of the dorso-lateral and ventro-lateral ganglia.
It is throughout part of its extent (fig. 9) wedged in between the dorso-lateral ganglion and the ventro-lateral ganglion, to be described in the next section, and its posterior end comes closely into contact with the auditory. The geniculate ganglion is double in composition. The posterior portion, derived from the neural crest, is definitely outlined and circular in form and seems to be purely general visceral in composition. The anterior end, which contains cells derived from the placode, is less regular in form and incloses or has attached to its ventral surface and resting directly upon the endoderm of the pharyngeal pocket a mass of cells which projects laterally giving a comma" shape to the ganglion in transverse section( fig. 8). The laterally projecting mass is derived from the epibranchial placode and can be distinguished both by its color and position of its cells. The
14 F. L. LANDACRE
placodal cells represent the special visceral portion of the ganglion while the remainder is general visceral. This placode is to be followed in detail later as well as similar cells in the IX and X, and will not be described more fully here.
Two nerves arise from this ganghon. The truncus hyomandibularis arises from the ventral border of the ganghon about one-third of its length from the anterior end and runs ventrolaterally from its point of origin.
The truncus hyomandibularis contains laterahs fibers derived from the ventro-lateral ganglion in addition to those derived from the geniculate. At the level of the floor of the pharynx it divides into two rami, the dorsal (ramus mandibularis) turning cephalad and the ventral ramus (ramus hyoideus faciahs) running directly ventral.
A second smaller nerve (the ramus palatinus faciahs) arises from the anterior end of the ganglion and pursues the course usual in teleosts following the roof of the pharynx and oral cavity forward to the level of the olfactory capsule. It seems to be accompanied throughout the proximal part of its course by the motor trunk of the facialis which supplies the muscle adductor arcus palatini and the relation of the two components at their exit from the ganglion is somewhat peculiar, in some series the visceral fibers having the appearance of entering the lateral line ganglion (ventro-lateral). In other series of the same age, however, one can trace the visceral component into the anterior end of the geniculate while the motor component passes further caudad and enters the ganglion from the ventro-mesial side where it joins the motor trunk running out with the truncus hyomandibularis.
The ventro-lateral VII
This ganghon (figs. 1 and 9), as I have identified it, lies on the mesial side of the anterior third of the geniculate, partially inclosed in a crescent shaped depression of the geniculate. This ganglion has a very characteristic appearance. The interior of the ganglionic mass is usually free from nuclei, all the cells being arranged radially with the small ends directed centrally (fig. 29).
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 15
The whole ganghon in embryos of 10 mm. is not usually more than one-third as long as the geniculate, but this ratio varies, since the ganglion is sometimes triangular with the smaller end extending back into the truncus hyomandibularis. In older embryos the ganglion is always triangular and the posterior end grows posterior and ventral to the geniculate, thus simulating the relations in Menidia (Herrick, '99), although the greater portion of the ganglion retains its position mesial to the geniculate. The fibers coming from the ganglion, mentioned in the preceding section as running out in the hyomandibular nerve, arise from the extreme posterior end of the ganglion and run into the hyomandibular on the ventral surface of the visceral fibers. The root arises here also and arches around the mesial surface of the geniculate ganglion and enters the medulla along with those of the dorso-lateral ganglion.
The position of the ventro-lateral ganglion in Lepidosteus differs from the position in Menidia (Herrick, '99) and in the embryo of Ameiurus (Landacre, '10) and in the Amphibia Coghill ('02 and '06). In the embryo of Ameiurus (56 hours) the ventro-lateral ganglion lies posterior to the geniculate, in Menidia posterior and mesial, while in the urodeles it is lateral (external) to the geniculate. There seems to be.no other case recorded where it is directly mesial to the geniculate.
The fact that the nerve components have not been worked and consequently one cannot trace the ganglion back to this stage from an older series, renders the identification of this ganglion more difficult than in such cases as the Gasserian and dorsolateral, where the ganglia are distinct and their nerves contain only one component which can be traced to its peripheral distribution.
Since, however, the placodal portion of the geniculate is quite distinct and its history can be traced, it becomes an important factor in the differentiation of the geniculate and ventro-lateral ganglia. Notwithstanding the rather unusual position of the ganglion identified as ventro-lateral, the following facts seem to warrant the identification:
(a). The two ganglia are quite distinct histologically. .
16 "' F. L. LANDACKE
(b). The epibranchial placode is added to the one identified as geniculate, or general visceral, as in the IX and four branchial ganglia of the X.
(c). The ramus palatinus, which does not contain lateralis fibers in an}^ type, arises from the geniculate.
(d). The ganglion identified as ventro-lateral seems to send all its fibers into the hyomandibular.
(e) . In the later stages of the ventro-lateral ganglion it assumes a position more ventral and posterior to the geniculate as in Menidia and in Ameiurus.
The auditory ganglion
The auditory ganglion (fig. 1) is a large comma-shaped mass with the large end directed forward and the smaller end extending caudad. The large anterior end is closely attached to the posterior end of the geniculate and to the ventro-lateral VII. The root enters the medulla from the anterior end and a fibrillated trunk enters the auditory capsule at the middle region of the ganglion.
The glossopharyngeus- ganglion {petrosal and lateralis portion)
This ganglion (figs. 1 and 10) is club-shaped with the large end projecting forward and downward and is attached at its extreme anterior end to a mass of cells (placode II) proliferated from the ectoderm at the posterior and dorsal portion of the pharyngeal pocket of the first true gill. The posterior attenuated portion arches up around the posterior surface of the auditory capsule and enters the medulla at a point almost directly dorsal to the anterior end of the ganglion. Just before it enters the medulla it passes into a well defined mass of cells. This is not a ganglion however, since in later stages there are no ganglion cells in this position and the thickness of the root at this point as shown in fig. 1 is undoubtedly due to the exit of motor fibers and the presence of the root of the lateralis X ganglion which enters at this point. After the lateralis X root becomes more completely
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTFUS 17
medullated the appearance of the proximal portion of the root of the IX changes completely and there is no connection between IX and X except through the lateralis X root which runs forward as in Ameiurus from the lateralis X ganglion to enter near the entrance of the IX root.
The glossopharyngeal ganglion contains three components, (1) the general visceral, (2) the placodal (special visceral or gustatory) and (3) lateralis cells. The lateralis portion of IX, in the 10 mm. stage and in preceding stages, is quite distinct in outline from the visceral portion and occupies the dorso-lateral portion of the IX and can be positively identified by the ramus supratemporalis which innervates a lateral line organ lying just lateral to the ganglion in the same transverse level. The anterior portion of the ganglion is composed of general visceral cells derived from the neural crest, and of the placodal portion which can be distinguished both by color and form of cells, while the posterior portion is composed of the general visceral cells and lateralis cells. Two nerves are present at this stage; the truncus glossopharyngeus, arising from the anterior end of the ganglion and running ventrally into the first gill bar and containing probably both general and special visceral fibers, and a lateral line nerve, ramus supra-temporalis, arising from the middle of the ganglion and running laterally to innervate at least one lateral line organ of the body line which I take to be the second organ of this line.
The vagus ganglia
This complex (fig. 1) contains at this time three chief ganglionic masses (a) the. lateralis X ganglion, (b) the first branchial ganglion and (c) a large poorly differentiated ganglion corresponding to the primordia of the general visceral (nodosal) and three remaining branchial ganglia. This last mass comes into' contact with the third gill slit and contains cells contributed by the third placode (counting the placode of the VII as no. 1) and its posterior end is not clearly definable. There is no definite jugular, or general somatic, ganglion present at this time. It can be detected first in my series in a 13 mm. embryo as a
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 1
18 F. L. LAXDACRE
small ganglion hing on the root of the vagus intracranially. At this time its ganghonic cells cannot be distinguished from embryonic sheath cells.
The lateralis X
The laterahs X is the best defined gangUon of the vagus group. It is an elongated cyhndrical mass of cells with its anterior end reaching the posterior end of the first branchial ganghon of the vagus and its posterior end reaching posterior to the caudal end of the ^4sceral X. It is situated laterallj^ in the body at the level of the notochord and hes between the skin and the branchial gangha of the vagus. I can detect only two fibriUated nerves arising from it at this time. The chief nerve (ramus lateralis vagi), arises from the posterior end of the ganghon and runs posteriorly as usual in teleosts. The second nerve is the ramus supra-temporahs vagi which arises from the anterior end of the laterahs X ganghon and passes directly lateral and slightly forward to a lateral hne organ apparentlj^ the third organ of the body lateral line.
The root of this ganghon does not enter with the vagus roots but pursues a course diagonally forward and upward to the region of the root of the glossopharjmgus with which at this stage, it enters the meduUa. In older embryos the fibrillated root of the lateralis X passes bej^ond the visceral root of the IX and enters the meduUa anterior to that root.
The branchial ganglia of the vagus
The first branchial ganglion of the vagus (figs. 1 and 11) is a visceral ganghon composed of cells derived from the neural crest (general \Tlsceral) and of cells derived from the placode of the second true giU (special visceral or gustatory). In shape it resembles the glossopharyngeal but has a position more nearly vertical in the body. The ventral end is the larger and it curves dorsally and at this stage comes into contact at its dorsal and posterior border with the remaining portion of the general visceral mass of the X. It is convex on its anterior face. The
THE EPIBRANCHIAL GANGLIA OP LEPIDOSTEUS 19
root of this ganglion enters the medulla along with the remaining visceral roots of the X. One fibrillated nerve is present (truncus branchialis vagi I). It arises from the anterior ventral end of the ganglion just behind its attachment to the placode and runs ventrally into the second true gill bar.
The remainder of the visceral X is not differentiated into branchial ganglia. It is an elongated mass of cells lying somewhat ventrally and mesially to the lateralis X. Its posterior end as mentioned above is ill defined. Its middle portion is attached to the placode (placode 4) and one branchial nerve (truncus branchialis vagi II) arises from it just posterior to its attachment to the placode. This ganglionic mass differentiates later into the three remaining branchial ganglia of the X having the same composition as the first branchial of the X and consists of general visceral cells derived from the neural crest and special visceral or gustatory cells derived from the placodes.
The root of this ganglion passes dorsally along with that of the first branchial ganglion and part of its fibers enter the medulla directly over the ganglion. Many of the fibers, however, at this stage pass further posterior forming a bundle lying near the medulla and enter the medulla posterior to the posterior end of the ganglion.
DETAILED DESCRIPTION OF THE EPIBRANCHIAL PLACODE OF THE VII IN THE 10 MM. EIVIBRYO
This placode is completely detached from the epidermis in the 10 mm. embryo, as mentioned above. After describing it in this stage its later history will be followed first, and then the mode of origin will be taken up.
After detachment from the epidermis, the placode occupies the anterior end of the general visceral ganglion of the VII nerve (fig. 1). The posterior and middle portions of the geniculate are round in transverse sections. The anterior third is indented on its mesial side by the ventro-lateral lateralis ganglion (figs. 20, 21 and 27). The extreme anterior end varies a good deal in shape in different series owing to the varying relations of the
20 F. L. LANDACRE
general visceral and placodal portions to each other. The general visceral portion sometimes extends farther forward than the placodal portion, sometimes both general visceral and placodal portions are of equal length and the anterior end of the ganglion is split (figs. 14, 15). In all series of this stage the anterior end consists of a mesial rounded portion and of a lateral spur resting on the endoderm of the hyoid gill pocket and extending somewhat dorso-laterally toward the epidermis (figs. 16 to 20). A portion of the median rounded mass and all of the lateral spur are derived from the placode. The manner in which the placodal portion joins the general visceral varies in different embryos somewhat. The visceral cells may lie like a cap dorsal, mesial and sometimes lateral to the placodal cells. In later stages the placodal cells are usually surrounded by the general visceral cells in this manner, but the condition shown in figs. 14 to 21 is the usual one in the 10 mm. stage, so that the placodal portion of the ganglion begins at the extreme anterior end of the ganglionic mass (fig. 14) becomes broader a few sections posterior to this point and possesses a large lateral spur (figs. 17 to 19) and disappears a few sections posterior to the anterior end of the ventro-lateral lateralis VII.
The placodal portion of the ganglion can be distinguished from the general visceral by the difference in staining reaction, the placodal portion usually being much darker (fig. 26) and can be distinguished further, by the arrangement of the cells, the placodal cells being elongated in the direction in which they have moved into the gangHonic mass. The mos^ uniform and most easily recognized characteristic is that of color (figs. 26, 28, 30, 31).
Posterior to the placodal portion of the geniculate ganglion we find the general visceral and ventro-lateral and dorso-lateral portions only (fig. 27). The ventro-lateral ganglion lies mesial and quite close to the geniculate and usually imbedded in it. It is a short round ganglionic mass with its cells usually arranged in a rosette with the nuclei situated peripherally. The geniculate ganglion has a totally different appearance, consisting of a rather dense mass of cells irregularly arranged and having very indefin
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 21
ite cell boundaries (figs. 26, 27, 28). Posterior to the ventrolateral lateralis ganglion, the geniculate is uniform in structure and passes dorsally and posteriorly toward the medulla accompanied by the root of the ventro-lateral ganglion. The posterior end of the geniculate ganglion is closely attached to the auditory ganglion, and near its entrance into the medulla, is joined by the root of the dorso-lateral lateralis ganglion; so that all the roots of the VII ganglion come into contact with the medulla near the same point and quite close to the entrance of the root of the auditory. The ganglionic complex of the VII has in general an arrangement quite characteristic for the Ichthyopsida (Herrick, '99, Landacre, '10) with the exception that it is quite easy at this stage in the development of Lepidosteus to separate the placodal or special visceral component from the neural crest or general visceral portion of the geniculate.
The relation of the placodal portion of the VII ganglion to the endoderm of the hyoid gill pocket is of the greatest importance in forming a clear conception of the mode of origin and detachment of the placode. The hyoid gill pocket as it approaches the ectoderm gives off at this stage two solid processes of cells neither of which come into contact with the epidermis (figs. 14 to 16), but from an early stage up to the 8.8 mm. stage both these processes are in contact with the epidermis. As they withdraw from the epidermis there appears a rather dense mass of mesoderm between the two processes and in the area between the processes and the ectoderm (fig. 19). This mass of mesoderm later develops into the hyomandibular cartilage and muscles associated with this cartilage and the ear capsule. The dorsal process lies farther forward, considerably anterior to the anterior end of the geniculate ganglion. At the anterior end of the geniculate it has the appearance shown in figs. 14, 15, 16. The primordium of the hyomandibular cartilage lies between the hyoid pocket and the epidermis in a recess formed by the dorsal and ventral prolongations of the endoderm and extends forward from this point. Four sections posterior to fig. 14 the ventral prolongation becomes detached and seems to disappear later, at the same time the dorsal prolongation becomes shorter and seems to detach a mass of
22 F. L. LANDACRE
cells which also disappear later. The placodal portion of the ganglion always rests upon the dorsal endodermic prolongation and in earlier stages is in continuity with the ectoderm at the posterior end of the dorsal endoderm process and abuts against it as shown in model (fig. 33). In the 10 mm. embryo where the placode is no longer in contact with the ectoderm and is separated from it by the primordium of the hyomandibular cartilage it still rests upon this dorsal pocket. The later history of the placodal cells is closely associated with this pocket.
THE LATER HISTORY OF THE PLACODE OF THE VII
The later history of the placode may be summarized briefly as consisting of (a) the withdrawal from the epidermis and incorporation into the geniculate ganglion, and (b) the reduction in number and the metamorphosis of the numerous compact placodal cells into ordinary ganglion cells that cannot be distinguished from cells of the geniculate ganglion derived from the neural crest. As to the withdrawal from the epidermis, a comparison of figs. 22, 23, 24, 25, with figs. 17, 18, 19 will show that the placodal spur of the geniculate ganglion nowhere approaches so closely to the epidermis as in the earlier stage. Fig. 25 shows also that the posterior end of the lateral spur extends caudad from the ganglion and lies, as an elongated n^ass of cells, small and dark staining like the placode, upon the endoderm of the hyoid pocket. The appearance of the posterior extension of cells is usually like that in fig. 25. The appearance of the caudal prolongation changes slowly. It is gradually withdrawn into the ganglionic mass of the geniculate. Fig. 30 illustrates the condition at the middle of the placodal mass and fig. 29 illustrates the condition five sections caudad where there are no placodal cells in the ganglion but the posterior spur is present (12.4 mm.). In stage 13.5 mm. there is no longer any posterior projection of placodal cells although the placodal cells reach the ventral surface of the ganglion (fig. 31).
The later history of the placodal cells is rather peculiar. They are the most striking feature of the facialis complex. The cells
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 23
as mentioned above stain a deep blue and in addition are quite small and closely packed. In a 24 mm. embryo they can be identified still, although reduced in numbers, and they seem to be represented in a 44 mm. and even in a 6-inch Lepidosteus. That they should remain so long undifferentiated is striking, but there can be no doubt as to the continuity of this mass of cells and that they are derived from the placode. That they are gradually transformed into ganglion cells seems evident from the conditions in the older series where they are of various sizes and some of them are evidently ganglion cells.
In a 24 mm. embryo the number of undifferentiated placodal cells is much reduced and there are groups of similar small cells in the posterior portion of the Gasserian, so that the minute cells are not peculiar to the placodal ganglion. The process of differentiation seems to take place on the periphery of the placodal cells where they are in contact with the normal ganglion cells. Since some placodal cells remain undifferentiated up to the 6-inch stage, it is possible that they may never be converted into normal cells, although this is improbable. The transformation of these placodal cells into ganglion cells is roughly correlated with the relative time of appearance of the placodal ganglia. They are the last ganglia to be formed and it is not surprising that they should transform into normal cells much later, but it is a little surprising that they should be delayed so long in their transformation.
THE ORIGIN or THE EPIBRANCHIAL PLACODE QF THE VII
The determination of the exact time of appearance of the epibranchial placode of the VII nerve is rendered difficult by the presence of three associated structures, viz; the preauditory placode, the thickening of the epidermis at the point where the hyoid endodermic gill pocket joins the epidermis, and lastly the presence of the anterior end of the geniculate ganglion which ends at the point where the epibranchial placode is formed, rendering difficult the identification of detached groups of cells lying in this immediate region.
24 . F. L. LANDACRE
The preauditory placode is the first of these to appear and consists, as in Ameiurus (Landacre, '10), of a forward continuation of the thickening of the epidermis which forms the auditory vesicle. This thickening (including preauditory placode, auditory vesicle, and post-auditory placode) in its early stages is much longer than the auditory vesicle which is formed in its middle region and its anterior end can be traced forward in the epidermis as a thickened column of cells to the region of the hyoid gill pocket. As in Ameiurus, this preauditory placode is modified in its anterior end and seems to disappear as a preauditory placode, but the posterior portion of it persists to a relatively late stage and is closely associated with, although probably not genetically related to, the epibranchial placode of the VII nerve. Before the appearance of a placode, or at least before the proliferation of cells begins to form the epibranchial placode, the preauditory placode seems to be continuous at its anterior end with the thickening of the epidermis at the point of contact of the endoderm of the hyoid gill pocket with the ectoderm. The preauditory placode (which is presumably the earliest trace of the dorsolateral placodes of the authors) seems to be continuous with the ectodermic thickening of the gill pocket up to 82 hours, but no thickening of either gill pocket or preauditory placode extends beyond the hyoid gill pocket.
The preauditory placode shows, in its posterior part particularly, an arrangement of its cells characteristic of early stages in the auditory vesicle and of lateral line organs. The cells are radially arranged but the placode does not show these characteristics as it approaches the hyoid gill pocket (fig. 35).
The thickening of the epidermis at the point where the endoderm of the hyoid gill pocket joins the ectoderm is the most conspicuous feature of the hyoid region up to the time that the epibranchial placode appears (fig. 34). The significance of this thickening is, uncertain. It may be due simply to the stimulus furnished by the contact of the endoderm with the epidermis, but is much more pronounced than in Ameiurus and consequently obscures the early differentiation of the epibranchial placode as well as renders it difficult to determine the exact relation of the
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 25
preauditory placode to both the epibranchial placode and the supra- and infra-orbital lines.
The cell arrangement of this thickening presents certain definite histological characters, the most conspicuous of which is the fact that it can be distinguished readily from the endoderm by the darker stain taken by the ectoderm, apparently due to the smaller size of the cells, the more compact and irregular arrangement, and the earlier loss of definite cell boundaries. These characters make it easy to trace the line of demarkation in most preparations between endoderm and ectoderm.
The third structure that must be constantly kept in mind in tracing the history of the placode is the position of the anterior end of the general visceral (geniculate) portion of the VII ganglion. This mass of cells, indefinite in outline as are all neural crest ganglia in their early stages, lies at the level of the hyoid gill pocket between the posterior end of this structure and the auditory vesicle and extends forward from the auditory vesicle to the posterior portion of the endodermic gill pocket. It is thus seen to be a mass of cells whose anterior end is wedged into the pocket formed by the withdrawal of the posterior end of the gill pocket from the ectoderm, and it is at this exact point that the ectoderm proliferates cells mesially to form the placode; so that the difficulty that has been found to exist in the interpretation of the relation of placodal cells to neural crest cells in other types occurs here with the exception that one can be certain that the neural crest portion of the VII (general visceral ganglion) does not form a contact with the epidermis. The difficulty arises in determining if a given group of cells which one finds in the anterior end of the geniculate came from the forward extension of the geniculate or from the placode. When these cells come off en masse and are numerous, no difficulty is presented but the determination of the source of small groups of cells, as in fig. 37, does present a difficulty. In the later stages of the formation, the placodal cells are detached from the epidermis in a large compact cluster, which can be distinguished from neural crest cells, so that the tracing of their ancestry is easy; but in the early stages of the formation of the geniculate ganglion this
26 F. L. LANDACRE
is not true owing to the indefinite outlines of both the placode and general visceral ganglion.
Since the placode begins by the proliferation of cells mesially at the posterior end of the hyoid gill pocket and at the anterior end of the preauditory placode, it can be seen readily that it is only when the process of prolification has reached a somewhat advanced stage that the placode can be definitely identified. Conditions in Ameiurus are somewhat simpler (Landacre, '10). There the preauditory placode does not persist in the region of the hyoid pocket up to so late a period and there is a definite histological change in the region of the pocket before the process of proliferation begins, and further there is no such marked thickening of the epidermis in the region of contact of ectoderm and endoderm as in Lepidosteus. However, aside from the presence of pronounced sensory fines, the primordia of the lateral lines, there is no striking difference between the two types, the persistence of the anterior end of the preauditory placode and the great thickness of the ectoderm being minor differences.
A fourth structure, the posterior extension of the epibranchial placode, should be mentioned in connection with the three just described. In the case of the IX and Xth ganglia it presents no difficulties, since the posterior extension of the epibranchial placode lies at a lower level and is quite distinct from the dorsolateral placode or primordia of the lateral lines.
In the VII, however, this is not true. The posterior extension of the epibranchial placode lies in the same plane approximately as the preauditory placode. In the early stages of the epibranchial placode the preauditory placode extends forward to the hyoid gill. Later, as the preauditory placode recedes toward the ear, the epibranchial extends backward toward the ear in the same plane as that occupied by the preauditory.
The most probable interpretation of the relation of the preauditory placode to the ectodermic thickening of the gill pocket, and of the epibranchial placode to both of these, is that the preauditory placode extends forward into the thickening of the ectoderm in the hyoid region and before the disappearance of the preauditory placode and during the maximum devc^lopment of the
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 27
ectodermic thickening the epibranchial placode appears. The later history of all three structures almost precludes the interpretation that their relations to each other involves more than juxtaposition.
The first probable trace of the appearance of the epibranchial placode is found in a 94-hour embryo. A section taken through the extreme posterior end of the contact of the hyoid endodermic gill pocket with the ectoderm (fig. 36) shows that the ectodermic thickening extends further mesially than it does anterior to this point and farther than in preceding stages. One section posterior to this (fig. 37) the endoderm has withdrawn completel.y from the ectoderm but the thickening is present and is continuous with an irregular mass of cells lying between the placode and endoderm. The proliferated mass of cells is continuous posteriorly with the neural crest (general visceral) portion of the VII. Mitotic figures are numerous between the cell mass and the placode indicating its origin from the placode. If this is true, however, the anterior end of the geniculate consists almost exclusively of cells derived from the placode since there is added to these cells later, the large body of cells that comes off en masse and is much more definite in outline.
In a 7.3 mm. embryo the epibranchial placode has reached a stage in its development such that it can be positively identified as the structure that later becomes detached en masse and added to the general visceral portion of the VII, since there is no break in its continuity from this stage up to the time of its detachment from the ectoderm. The ectoderm in the region of the placode is definitely differentiated into the primordia of the sensory lines, placode, and the thickening of the ectoderm at the attachment of the endodermic pocket. Throughout the length of the attachment of the endodermic pocket, and dorsal to the thickening of the ectoderm associated with this pocket, there is a second thickening incorporated more or less with the ventral thickening but distinguished from it by its rounded contour and by the arrangement of its cells. This dorsal thickening (fig. 38) is the primordium of the sensory lines anterior to the hyoid gill pocket. This line at this stage extends somewhat anterior to the hyoid
28 F. L. LANDACRE
gill pocket and also extends posterior to this point (figs. 39, 40) ; so that it extends backward past the point of origin of the placode.
The dorsal sensory line shown in figs. 39 and 40 extends onehalf of the distance from the hyoid gill pocket to the auditory vesicle, while the thickened area on which the placode forms extends two-thirds of this distance. This series is unusual, since in later series I cannot find a dorsal sensor}^ line extending posterior to the placode and lying dorsal to it.
The form and position of the placode is shown' in fig. 39. It consists of a well defined mass of cells projecting mesially and lying just ventral to the dorsal sensory line. Fig. 40 is taken four sections posterior to fig. 39 and shows the posterior extension of both the sensory line and the thickening which represents the posterior extension of the epibranchial placode and is continuous with the preauditory placode. The anterior end of the general visceral VII is more definite in outline than in the preceding stage figured, and comes into contact at its anterior end with the placode, although there is no difficulty in separating the two structures owing to the definite outhne of the placode. There is the doubt, however, as to the composition of this extreme anterior end of the general visceral ganglion mentioned above.
The changes in an 8 mm. embryo are not marked, consisting chiefly in the increase in size of the mass of cells proliferated mesially in the placode. It should be borne in mind that the anterio-posterior extent of the placode is usually not over three or four sections (24/^) thick, so that in transverse sections one passes from the endodermic prolongations of the hyoid pocket directly into the ectodermic prolongation of the placode. This thickness in the anterio-posterior extent of the placode seems to be due to its being apposed so closely to the posterior surface of the gill pocket and gives the placode when seen cut through its greatest transverse dimension, the appearance of being much larger than it is.
In fig. 41 the endoderm of the gill pocket characterized by its pale color and large cells with definite walls abuts directly against the dark staining small celled ectoderm so that the boundary line is quite definite. In fig. 41 the continuity of the gill pocket
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 29
and ectoderm is not broken but at least half of this is formed of ectoderm and the ectodermic cells at the base of the proliferated mass are in active mitosis.
In fig. 42 the endodermic pocket has withdrawn from the ectoderm and the placodal mass projects freely into the mesoderm. One section posterior to this point the placodal mass is shorter and posterior to this is present as a slight ridge in the ectoderm. The condition just described, i.e., a thin flat placodal proliferation of cells closely apposed on its anterior surface to the posterior wall of the hyoid gill pocket and usually extending through not more than four sections, is so constant that it is unnecessary to follow it in detail further than to give sections through the placode at its maximum size. Between the 7.3 mm. stage and the 8 mm. stage the general visceral portion of the VII has grown forward as shown in fig. 42 until it lies upon the dorsal surface of the posterior end of the hyoid gill pocket. This change in position of the anterior end of the ganglion carries the ganglion anterior to the point at which the placode originates; so that the placodal cells are added in such a manner that they work their way into the general visceral mass or are surrounded by the visceral cells; at any rate they are incorporated into the general visceral ganglion.
In the 8.3 mm, stage (fig. 43), both the placode and the anterior end of the general visceral VII have increased in size. The general visceral ganglion is irregular in outline and it is difficult in this particular series to tell how much of the complex is placodal. Mitotic figures are numerous both in the ganglion and in the placode. The dorso-lateral VII ganglion is present in fig. 43 but the section is taken just anterior to the ventro-lateral VII.
The changes in the placode, aside from its darker color, are almost imperceptible between the 8.3 mm. stage and the 9.5 mm. stage (figs. 32 and 33). The general visceral portion of the geniculate, however, becomes more definite in outline and compared with the placodal portion of the ganglion, is much lighter in color and the cells are larger and more loosely arranged. Between the 9.5 mm. stage and the 10 mm. stage which has been fully described, the placode becomes cornpletely detached from
30 F. L. LANDACEE
the ectoderm in most series. In the process of becoming detached the placode seems to break near the epidermis and does not leave the epidermis of normal thickness at the point of detachment. The presence of loose masses of mesoderm cells in the region of the placode and particularly the presence of the primordium of the hyomandibular cartilage and associated muscles render it difficult to determine the exact time of detachment even though it were constant. The thickening of the epidermis after the placode is completely detached extends from the posterior end of the placode to the level of the anterior border of the auditory capsule. While this thickening does not confuse the relation in the hyoid region during the later stages of the placode, it is of the greatest importance to determine its early history and exact anatomical relations with reference to the dorso-lateral sensory lines.
SUMMARY OF THE HISTORY OF THE FIRST EPIBRANCHIAL
PLACODE
The epibranchial placode of the VII nerve in Lepidosteus can be identified first as a definite structure whose history can be followed consecutively, at about the age of 94 hours after fertilization. It appears as a mesial proliferation of cells from the ectoderm just posterior to the endodermic pocket of the hyoid gill to whose posterior surface it is closely attached. The placode appears to be the posterior portion of the ectodermic thickening with which the endodermic hyoid pocket comes into contact. It is also apparently continuous posteriorly with a thickened ridge of cells, the preauditory placode, extending back to and in early stages being continuous with the anterior end of the auditory vesicle. Both the preauditory placode and hyoid ectodermic thickening are present before the placode appears and they are continuous with each other. As the placode grows mesially it comes into contact with the anterior end of the general visceral portion of the geniculate ganglion, with which it fuses, sometimes being attached on the lateral portion of the geniculate, sometimesto the ventral portion, and sometimes being
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 31
surrounded by general visceral cells. After growing mesially and coming into contact with the general visceral ganglion at about the age of 94 to 100 hours, it becomes detached from the ectoderm when the embryo is somewhat less than 10 mm. in length. At the point of detachment there is left a cell mass which extends backward to the region of the ear.
Preceding and for a long time after detachment, the placodal cells are sharply differentiated from the remainder of the geniculate cells. As late as the 44 mm. stage and probably as late as the 152 mm. stage some of the placodal cells are differentiated by their small size and intense dark color. The number is constantly reduced, however, and similar small dark staining cells can be detected in other ganglia particularly the Gasserian, so that the fact that one can trace the history of these cells to so late a period is probably due to their late differentiation into normal ganglion cells.
Just how much of the geniculate ganglion at any stage after the detachment of the placode and after the metamorphosis of the small placodal cells into normal ganglion cells, may be general visceral and how much may be special visceral cannot be determined, but the late differentiation of these placodal cells enables one to locate them and follow their history before metamorphosis much more completely than in any type described.
The relation of the early stage of this placode to the dorsolateral sensory lines needs a more careful study than can be given the question in connection with the later history of the placodes. The presence of definite sensory lines resembling those of the sea bass (Wilson, '91) shows that the lateral line system, at least in its earlier stages, resembles Serranus much more closely than Ameiurus, but whether these sensory lines are continuous with the anterior end of the auditory thickening (preauditory placode of Ameiurus, Landacre, '10) or not must be taken up separately. The presence of epidermal thickenings or sensory lines, lying at the same level as the preauditory placode or dorso-lateral sensory line, but not identical with it, as a study of the epibranchial placodes of the IX and X nerves shows, emphasizes the necessity of exercising caution in order not to confuse these dorso-lateral
32 F. L. LANDACRE
sensory lines with ventro-lateral sensory lines when they lie at the same level and apparently are continuous the one with the other.
THE EPIBRANCHIAL PLACODE OF THE IX NERVE
The placode of the IX nerve resembles the placode of the VII in its mode of origin, detachment, and incorporation into the general visceral ganglion. It is much smaller, however, and occupies less time in the transition from ectoderm into ganglion cells. The difficulty in determining the time of appearance of the placode of the IX is in part the same as that encountered in the VII. Owing to the angle at which the gill meets the roof of the pharynx, the ectodermic invagination in the region of the IX is more extensive and projects further caudad relatively than in the VII and until there is some structural or color differentiation in this mesially projecting mass, the identification of the placode is almost impossible. The relation of the general visceral IX to the placode is exactly like that in VII. The general visceral ganglion projects cephalad to the point where the placode forms, and ends in most series between 8.8 and 9.9 mm. just at the mesial tip of the placode; sometimes, however, it projects farther cephalad as it always does in series older than 9.9 mm. and its anterior end rests upon the ectodermic invagination.
The difficulty found in the VII in regard to the relation of the sensory line to the placode does not exist here. The post-hyoid sensory line (dorso-lateral) extends beyond the anterior end of the IX ganglion but does not reach, as a definitely differentiated column of cells, the posterior end of the auditory vesicle. .This sensory line lies dorsal to the placode and entirely detached from it so that there can be no doubt that the two structures are quite distinct and the condition here strengthens the opinion expressed in discussing these conditions in the VII, that the relation of the preauditory to the epibranchial placode was one of contiguity only and due to the fact that in the forward growth of the preauditory placode it occupies the same level as the epibranchial placode. This conclusion is still further strengthened from the study of Ameiurus (Landacre, '10) where the degeneration of
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 33
the anterior end of the preauditory placode could be followed preceding the appearance of the epibranchial placode. The relative position of the placode, general visceral IX, and ectodermic wall of the gill, are shown in text-figs. 1, 2, and 3 (p. 34). The first positive trace of the placodal cells was found in an
8.8 mm. embryo. This is shown in fig. 44. It differs somewhat from the early condition usually found, in that the ectodermic invagination of the gill pocket extends mesially to the placode and some cells projecting from the ectoderm in the region of the anterior end of visceral IX do not stain like placodal cells and are not genetically continuous with placodal cells. The reason for the greater extent of the ectodermic invagination in the IX, as well as in the first two branchial X, is the more acute angle at which the gill joins the roof of the pharynx.
The placodal cells are usually found immediately posterior to the ectodermic invagination of the gill pocket. However, there are ectodermic cells not belonging to the placode situated mesially to the placodal cells. The ectodermic gill invagination forms a curved mass reaching from in front of the placode to the mesial side of the placode of the IX. The placodal cells seem to have pushed their way into the posterior end of the ectodermic gill invagination. One section anterior to fig. 44 the placodal cells are absent and one section posterior to this point the section passes through into the general visceral ganglion which is barely in contact with the epidermis. It is thus seen that at this stage the placode in its anterior-posterior extent is quite thin, as are all the placodes in Lepidosteus. Between the 8.8 mm. and the
9.9 mm. embryo this mass of placodal cells cannot be identified always but in the 9.9 mm. embryo they become permanently established and their continuity can be traced up to the time they become detached from the ectoderm and incorporated into the general visceral IX.
In a 9.7 mm. embryo (fig. 45) we find the usual form of the placode. It consists of a mass of cells projecting mesially from the epidermis with the thickest portion of the placode lying ventral to the point of attachment. Mitotic figures are numerous in both the placode and the epidermis. On its anterior surface it
THE JOURNAL OF COMPAHATIVE NEnROLOGY, VOL. 22, NO. 1
34
F. L. LANDACRE
1 X-TO
2 XJ-0
L.L.
3 xso
Text figures 1, 2 and 3 are camera tracings through the region of the IX gill
from a 9.7 mm. embryo of Lepidosteus.
Fig. 1 passes through the point of contact of the first true gill with the roof of the pharynx.
Fig. 2 passes through the ectodermic gill shelf (ec.) seven sections posterior to fig. 1
Fig. 3 passes through the epibranchial placode of the IX and through the anterior end of the general visceral IX. The resemblance stucturally between the ectodermic gill shelf and the placode is striking. The placode can be recognized by its darker color.
Aud.V., auditory vesicle; Aud., auditory ganglion; B.V. blood vessel; Br. A, branchial artery; E.P.IX, epibranchial placode of IX; Ec, ectoderm of gill shelf; G.V.IX, general vi.sceral ganglion of IX; Met., Metencephalon; No., notochord; Pr.L.L., primordium of lateral line.
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 35
abuts against the ectodermic gill invagination and on its posterior surface it abuts against the anterior end of the general visceral IX. It is thus wedged in between the ectodermic gill invagination and the general visceral portion of the IX. From the 9.9 mm. stage on, the anterior end of the IX grows forward so that it rests upon the shelf formed by the ectodermic gill invagination. In some embryos younger than the 9.9 mm. stage, cells are found on this shelf but it is a constant feature of the ganglion from this stage on.
In the 10 mm. stage, the ganglion has assumed the comma shape (fig. 46) consisting of a rounded mesial portion and a lateral projection extending toward the epidermis and resting upon the extreme posterior end of the ectodermic gill invagination. This lateral projection is not continuous with the epidermis, but one section posterior to the one figured it is continuous. It is not possible at this stage to distinguish accurately by color differentiation between the placode and the ganglion cells presumably of neural crest origin. Since, however, the placode is not yet completely detached from the epidermis, one can trace the derivative of the placode by the form of the cells and their continuity with the epidermis.
After the detachment of the placode from the epidermis the placodal cells become, as in the VII, sharply differentiated in color from the remainder of the ganglion. The general form of the placodal mass is quite similar to that of VII, consisting of a central core more or less incorporated into the general visceral and projecting laterally and caudally (figs. 47, 48). This spur of cells is incorporated into the ganglion and cannot be detected in the 13 mm. stage, but is present in the 12.4 mm. stage. The remnant of the mass of placodal cells can be found in the 24 mm. stage and similar small dark staining cells can be found in the anterior tip of lateralis X indicating, as suggested in the discussion of the similar condition in the trigemino-facial complex, that there is a delayed development of these cells and that in Lepidosteus, if the cells retarded in development happen to be aggregated, the appearance described above is found, since it occurs in both the Gasserian and lateralis X and is always found in the pla
36 F. L. LANDACRE
codal ganglia. As in the case of the VII, the number of undifferentiated placodal cells is apparently greatly reduced in the later stages of my series and one can find cells lying at the periphery of the incorporated placodal cells and consequently in contact with general visceral cells, intermediate in size between the small and large size of ganglion cells. The late differentiation of these cells is apparently correlated with the late appearance of the ganglia and taste buds as stated above.
THE FIRST EPIBRANCHIAL PLACODE OF THE X
There are four epibranchial ganglia on the X nerve, as is usual among the Ichthyopsida. They are smaller than that on the VII and correspond closely in size and position to the IX. There is, however, owing to the differences in size and position of the general visceral ganglia, to which the special visceral ganglia are added, considerable variation in shape. The difference in position of the last gills alters also the appearance of the placode, particularly its relation to the ectodermic invagination.
Reference to fig. 1 will show that the first branchial ganglion of X resembles the IX in general form, being an elongated mass of cells placed nearly vertical in the body with its dorsal extension joining the large body of cells which constitutes the larger portion of general visceral X. This large mass of cells which contains the remaining three branchial ganglia of X is not so definitely formed into branchial ganglia as in Menidia. There is, however, at the point where each placode is formed a mass of cells projecting ventrally, to which the placodal cells are added, so that, while the presence of branchiar divisions is indicated, the bulk of the general visceral cells is contained in one large general visceral ganglion.
The size of general visceral X and the fact that the branchial divisions are less marked give an appearance to the placodes that lends itself to the older interpretation of these structures, i.e., that they are epidermic thickenings with which the neural crest ganglia come into contact, but a careful examination of a series of embryos taken at close intervals shows that they resem
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 37
ble closely the conditions already described for VII and IX nerves and consist of proliferations of cells derived from the ectoderm and added en masse to the neural crest ganglia.
The first placodal ganglion of the X appears in a 10 mm. stage (fig. 49). It projects mesially from the ectoderm at the extreme anterior end of the general visceral X, of which it forms the most anterior portion. No portion of the first branchial X lies upon the ectodermic shelf at this stage. It also abuts against the posterior end of the ectodermic gill shelf, from which it can be distinguished by its color and the arrangement of its cells as well as by the fact that it becomes detached later.
The relation of the epibranchial placode to the dorso-lateral sensory line is similar to the condition in the IX. The dorsolateral sensory line lies somewhat dorsal to the placode and quite distinct from it. This placode is continued as in the IX posterior to the point of detachment by a thickened column of cells which disappears before reaching the next placode. Evidently the dorsolateral sensory line and caudal prolongation of the placode are quite distinct structures in both IX and first branchial X and must be reckoned with in the case of the VII also if one is to interpret correctly the structures lying in the region of the first epibranchial placode.
In the 10.9 mm. embryo the placode is attached to the ectoderm by a slender cord of cells only, the lateral prolongation described in the VII and IX. This lateral prolongation extends backward also. In the 11.5 mm. stage (fig. 50) the placode is completely detached from the ectoderm, although both the placodal cells and the general visceral cells of the ganglion are in contact with the ectoderm; in fact, the ganglion rests upon the lateral roof of the pharynx. Before the placode is detached from the ectoderm the color differentiation between placodal and general visceral cells is marked and continues to be marked in all my series up to the 24 mm. stage without so apparent a reduction in the number of placodal cells as is shown in the VII and IX. The later differentiation of the placodal cells here and in the remaining placodes of the X is to be expected on account of their later appearance as compared with the VII.
38 F. L. LANDACRE
THE SECOND EPIBRANCHIAL PLACODE OF THE X
The second epibranchial placode appears first in my series in a 10 mm. embryo (fig. 51). As in the case of the first epibranchial placode of the X, it lies at the anterior end of the corresponding general visceral branchial ganglion (fig. 1) and at the posterior end of the ectodermic shelf of the third true gill. It lies below the fmidament of the lateral line and it is continued caudad in a thickening of the epidermis which does not reach the next gill and is throughout its course entirely distinct from the fundament of the lateral line. Fig. 52 shows the condition of the placodal portion of this ganglion in a 10.9 mm. embryo. It is completely detached from the epidermis laterally but still rests upon the epidermis and has both the lateral and caudal prolongations. The later history of this placode parallels those already described and the placodal cells can be readily detected in my oldest series (24 mm.)
THE THIRD AND FOURTH EPIBRANCHIAL PLACODES OF THE X
The third epibranchial placode of the X appears first in my series in a 10.9 mm. embryo (fig. 53). It differs from those already described in being less pronounced both as to size and color differentiation. In some stages succeeding the 10.9 mm. the placodal cells are difficult to detect, although they can always be found if the approximate location of the placodal cells is determined with reference to the corresponding gill bar.
The appearance of this placode after detachment from the ectoderm and before complete incorporation into the general visceral ganglion and while still possessing the lateral and caudal spurs, is shown in fig. 54. The fundament of the lateral line is not present at the level at which this section is taken, owing apparently to the absence of a lateral line organ at this point, but slightly posterior to this point it is present and occupies a level above the epibranchial placode. The thickening of the epidermis running caudad from the point of origin of the epibranchial placode is not pronounced but is present. The later history of the placode, including its incorporation into the general vis
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 39
ceral ganglion, offers no new features. It can be detected in the 24 mm. stage.
The fom*th epibranchial placode of the X appears first in a 12.9 mm. embryo (fig. 55). The posterior surface of the fourth gill bar of the X does not become detached from the ectoderm but this does not alter the relations greatly. There is no ectodermic shelf and I can detect no thickening of the epidermis extending caudad from the point of origin of the epibranchial placode. The fundament of the lateral line in this region lies far dorsal at the level of the lateral line nerve of the X. This nerve lies on a level with the middle of the notochord. The later history of this placode duplicates the history of the preceding placodes described. The lateral and caudal prolongations are less pronounced but it becomes incorporated into the last general visceral branchial ganglion and can be located in the 24 mm. series.
GENERAL SUMMARY AND DISCUSSION
1. The epibranchial placodes of Lepidosteus osseus arise as proliferations of the ectoderm at the dorsal and caudal border of the corresponding gill bar. They project mesially and finally become detached en masse and fuse with the general visceral portions of the VII, IX and four branchial ganglia of the X nerve. The point on the general visceral ganglion at which the placodal cells join it is always near its anterior end, sometimes in such a manner as to form the extreme anterior tip of the corresponding ganglion, sometimes, however, joining it laterally and ventrally in such a manner as to be partly surrounded by the general visceral cells.
2. Preceding the detachment of the epibranchial placodes their history can be followed, owing to their continuity with the ectoderm, from which they differ both in color intensity and in histological character. In the earlier stages, however, especially in the case of the VII nerve whose epibranchial placode is by far the largest and most conspicuous of the series, difficulties arise because of the presence of othef thickenings in the ectoderm, i.e., (a) the primordia of the lateral sensory lines, (b) the thickening
40 F. L. LANDACRE
of the epidermis at the point where the pharyngeal endodermic pocket joins the ectoderm, (c) the anterior extension of the auditory vesicle (the preauditory placode of Ameiurus, Landacre, '10, the branchial sense organ of Wilson, '91), (d) the thickening of the epidermis extending caudad from the point of origin of the epibranchial placode.
In all the epibranchial placodes there is a thickening of the epidermis at the point where the endodermic gill pocket joins the ectoderm and this always lies anterior to the point of origin of the placode. The epibranchial placode always arises at the posterior end of this thickening and while in Lepidosteus the placodes are unusually long in their transverse axis they are thin from anterior to posterior and abut against the posterior border of the ectodermic gill invagination. In all the placodes except the VII, and sometimes here, there is a sharp color differentiation as well as histological differentiation between the two structures and one can be quite sure of this distinction in the later stages of the placode, although the two structures are continuous, when one reads the sections from the ectodermic gill shelf into the placode.
The primordia of the lateral sensory lines can be differentiated from the epibranchial placodes with equal ease except in the case of the VII. They lie at a different level, much above the placodes in IX and X, but in VII the supra-orbital, sub-orbital and mandibular sensQry lines converge at the hyoid gill rendering it difficult to differentiate between primordia of lateral sensory lines and the early stage of the epibranchial placode. Much the same difficulty exists in the VII with reference to the preauditory placode. This structure in its anterior extension drops to the level of the hyoid gill and seems in the earlier stages, before the appearance of the epibranchial placode, to become continuous with the ectodermic gill thickening in this region although it changes its histological characters at the anterior end. To add to these difficulties in the case of the VII, each epibranchial placode in Lepidosteus is continued caudad by a thickening of the epidermis, which in the case of the IX and X ganglia lies at a lower level than the fundament of the lateral lines and of course in these cases cannot be confused with the dorso-lateral placodes.
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 41
In the VII the column of cells extending caudad from the epibranchial placode and persisting after the detachment of the placode occupies the same level in the epidermis as that previously occupied by the preauditory placode. There can be no doubt, however, from an examination of the epibranchial placodes of IX and X that this is a different thickening from either the preauditory placode or the primordia of the dorso-lateral sensory lines. I interpret all these as distinct structures, including the epibranchial placode and its posterior extension in the epidermis, the preauditory placodes and primordia of the sensory lines and the ectodermic thickening at the point where the endoderm of the hyoid gills joins the ectoderm, on evidence furnished by the study of similar structures in the IX and X ganglia; and I conclude that they are simply contiguous in the VII. As to the exact relation of the sensory lines to the preauditory placode, there is some degree of uncertainty in view of the conflicting evidence furnished by Wilson ('91) on Serranus and my own work on Ameiurus.
The significance of the posterior extensions of the epibranchial placodes is problematical also. They are certainly not closely related to the fundament of the lateral lines in the IX and X, being, in fact, entirely distinct from them. The whole situation emphasizes the extreme caution that must be exercised in making statements in regard to the relations of sensory lines lying in the region of the VII either epibranchial or dorso-lateral, and in particular in regard to the relation of the preauditory placodes to the supra-orbital, sub-orbital and mandibular sensory lines, since the point at which the preauditory placode is supposed to split up into sensory lines is in the region of the epibranchial placode of the VII, The hyoid gill region becomes the focal point in the differentiation of all these structures. The easiest of all these structures to follow is the epibranchial placode of the VII after it once becomes established, although it is difficult to locate in its early stages. The growth of all the placodes, including the VII, can be followed with ease to the time when they reach their maximum size. Both their structural and color differences are sharp. The placodes take a darker stain than either
42 F. L. LANDACRE
the epidermis or the general visceral ganglia and their cell arrangement is characteristic, the cells being closely packed with numerous mitotic figures. The body of the placode is apparently derived from the deeper nervous layer of the ectoderm ventral to the point of attachment. The ectoderm dorsal to the point of attachment of the placode is always thin.
3. During the time of detachment and throughout their later history the placodal cells can be followed for the same reasons; in fact, the placodal cells during their later history and up to the time they become metamorphosed into ordinary ganglion cells are more sharply differentiated from general visceral cells than in their earlier stages and present a striking feature in the ganglia of which they are components. The ease with which these placodal cells can be followed in Lepidosteus seems to be unique among the Ichthyopsida so far studied.
Immediately after the epibranchial placodes become detached from the epidermis and during the earlier stages of their incorporation into the general visceral ganglia they occupy the ventral or ventro-lateral portion of the corresponding ganglion and always have a spur of cells projecting laterally toward the epidermis at the point at which the placode became detached. This spur of cells always except in the case of the fourth branchial ganglion of the X projects caudally also.
In the later history of each ganglion this spur becomes incorporated into the larger mass of placodal cells which at first, while being largely surrounded by general visceral cells, always reaches the external boundary of the ganglion at its ventral surface. Still later in the history of each ganglion the placodal cells are found completely surrounded by general visceral cells or cells of the same type. At the boundary between the incorporated placodal cells and the surrounding general visceral cells there are found in embryos of 12.4 to 24 mm., especially in the VII ganglion, cells varying in size from that of the minute dark staining placodal cells to that of the ordinary visceral ganglion cells. This indicates that the placodal cells are gradually transformed into ordinary ganglion cells indistinguishable from general visceral ganglion cells. Some of these small dark staining cells persist
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 43
in the oldest of my series and there are such cells found in a 44 mm. embryo and even in a 152 mm. fish at approximately the point where the placodal cells should be, although my series are not continuous up to these older stages.
The fact that the history of the placodal cells can be followed so definitely seems to depend upon two things; first, the late appearance of the placodal ganglia as compared with the general visceral ganglia and the retarded development of the gustatory organs of Lepidosteus as compared with such a form as Ameiurus. This sets the immature placodal ganglion off in sharp contrast with the older and more mature general visceral ganglia. As the placodal cells become transformed into normal ganglion cells, they can no longer be distinguished from the general visceral cells.
In the second place, the identification of the placodal cells seems to depend upon the fact that in the ganglia of Lepidosteus the histological distinction between immature ganglion cells and mature ganglion cells is unusually sharp, so that if the immature ganglion cells happen to be aggregated they become, owing to their small size and dark staining properties, quite conspicuous. Such masses of cells can be found in a 24 mm. embryo in both the Gasserian and in the lateralis X ganglion but not in the earlier stages of these ganglia. Since there are no epibranchial placodes on these ganglia, these masses of cells are to be interpreted as immature cells. Such immature cells are usually found in ganglia but become especially prominent when collected in definite masses. The nerve fibers arising from ganglia containing both placodal cells and neural crest cells are not sufficiently different from each other in the oldest specimen examined (152 nun.) to enable one to trace the gustatory and general visceral fibers to their respective ganglion cells and peripheral terminations, so that for the present the reason for the classification of the placodal cells as special visceral cells must rest on the evidence offered in a later paragraph.
4. The explanation suggested in the body of the paper, that the observed difference between the placodal cells and the remaining cells of the general visceral ganglia of the VII, IX, and X nerves is due to the relatively late appearance of the gustatory
44 F. L. LANDACRE
organs, finds confirmation in a comparison of the relative time of appearance of the placodes and taste buds in Lepidosteus and Ameiurus (Landacre, '07).
Approximately the same time, five days, intervenes between the fertilization of the eggs and the time of hatching in Lepidosteus and Ameiurus. If we compare the size at any given age, and rate of growth for any given period, Lepidosteus is found not only to be longer but to grow faster than Ameiurus. At the age of 113 hours Ameiurus is 5.73 mm. long, while at the nearest corresponding age, 112 hours, Lepidosteus is 8 mm. long. Between the ages of 113 hours and 199 hours, Ameiurus increases 2.77 mm. in length, while Lepidosteus between the ages of 112 hours and 196, my nearest corresponding series, increases in length 5 mm. — a total difference in growth of 2.23 mm. in favor of Lepidosteus. During this period Ameiurus increases 43.3 per cent while Lepidosteus increases 62.5 per cent.
If now we compare the more rapid rate of growth in Lepidosteus with the time of appearance of preauditory placodes, the length of time intervening between the appearance of the first placode and the appearance of .the last, the time at which taste buds first appear, and lastly the total number of taste buds at any given age, we shall find all these processes beginning earlier and being completed earlier in Ameiurus, which is the slower growing form.
The first epibranchial placode appears in Ameiurus preceding the 49-hour stage and the last placode appears at 105 hours. In Lepidosteus the first placode appears at 94 hours and the last at 191 hours. There is a difference of 45 hours between the time of appearance of these structures and a difference of 41 hours in the time intervening between the appearance of the first and the last placode, the placodes appearing earlier and consuming less time in their formation in Ameiurus which measured by length grows slower than T^epidosteus. The first taste buds appear in Lepidosteus at 191 hours, 97 hours after the appearance of the first placode while in Ameiurus the first taste buds appear at 113 hours, 74 hours after the appearance of the first placode. So that here again the taste buds appear later and more time
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 45
intervenes between the appearance of the placode and the appearance of the taste buds in Lepidosteus than in Ameiurus, which is the slower growing form. Of more significance still, is the relative number of taste buds present at a stage when both types have them developed fully enough so that they can be counted with certainty. Two series fulfil these conditions closely, Lepidosteus at 214 hours and Ameiurus at 213. At the age of 214 hours, Lepidosteus has 32 taste buds distributed on the roof of the oral cavity and pharynx, and on all five gills. Owing to the large number of mucous glands on the outer surface of the body and the presence of the adhesive disc on the head where external buds are most likely to be found, it is not possible to determine the number in the skin.
In Ameiurus at 213 hours there are 146 taste buds in the oral cavity, 352 in the pharynx and gills and 117 situated externally on the skin of the head chiefly. This gives a total of 615 taste buds in Ameiurus as compared with 32 for Lepidosteus for a corresponding age. The later appearance and slower rate of growth of ganglia and limited number of taste buds in Lepidosteus as compared with Ameiurus of the same age seem to offer, when we consider the different rate of growth in the two types, strong evidence that the gustatory system of Lepidosteus is retarded in development as compared with other structures in this form and that this retardation is indicated in the histological differences between placodal and neural crest cells and offers a satisfactory explanation of the retarded metamorphosis of the special visceral cells into normal ganglion cells.
5. The assumption that cells derived from the epibranchial placodes, after their metamorphosis into ganglion cells, are the cells giving rise to fibers supplying taste buds and consequently designated as special visceral ganglia, rests upon indirect evidence but evidence of such a character as to warrant the assumption in view of the extreme difficulty of demonstrating its truth or falsity. Epibranchial placodes are found in all types of vertebrates, even among mammals, including man. Among the lower vertebrates where their history can be followed in series taken at close intervals, they can be shown in some cases to con
46 F. L. LANDACRE
tribute cells to the neural crest portions of the corresponding ganglia. In other types where the placodes are less prominent an actual contribution of cells to the neural crest portion of the corresponding ganglia has not been shown to take place, but a contact is formed between the neural crest ganglia and the epidermis in all cases. In view of the reduced character of the gustatory system in many forms as compared with the fishes, it is not surprising that the actual contribution of cells by the epibranchial placode should not be large and might take place during the period of contact and still be difficult to demonstrate. There seems to be no other adequate explanation for the formation of this contact between the neural crest ganglia and the ectoderm in such types that would harmonize with the known conditions in Ameiurus and Lepidosteus.
In all types epibranchial placodes occur on those nerves and those only, VII, IX and X, which contain gustatory fibers. Whenever, as is usually the case among the Ichthyopsida, the ganglia of these nerves are complex, containing lateralis, cutaneous and visceral components, the placodal cells join only the visceral ganglia, never the lateralis or general cutaneous ganglia. These visceral ganglia give rise to fibers supplying general visceral surfaces and taste buds only. In Ameiurus and Lepidosteus the various components of the ganglia are so distinct in the embryos that this conclusion can not be doubted and the problem resolves itself into the effort to differentiate special visceral or gustatory, and general visceral ganglia. Ganglia such as the profundus and Gasserian which do not contain visceral fibers of either type and have no epibranchial placodes, can be eliminated. With equal certainty we can eliminate all lateralis and general cutaneous ganglia in VII, IX and X, since they give rise to no visceral fibers of either type and have no epibranchial placodes.
An examination of the visceral ganglia of Ameiurus shows that the VII ganglion, which in the adult supplies a large number of taste buds, has a large placode, while the last branchial ganglion of the X which supplies in most types a limited number of taste buds, has a small placode. The visceral portion of the IX seems to be exclusively placodal in origin and seems in the adult to give
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 47
rise to gustatory fibers only. So that in general there is a close correspondence between the size of the epibranchial placode and the number of gustatory fibers to which the ganglion gives rise in the adult.
A study of Lepidosteus, in addition to furnishing a confirmation of the conclusion reached from a study of Ameiurus, shows in addition that the placodal ganglia maintain their integrity for a long time, although embedded in the general visceral ganglia, and that the late appearance of the epibranchial placodes and their slow metamorphosis into ganglion cells is closely correlated with the retarded appearance of the gustatory organs. This correlation, when taken in conjunction with the fact that only those ganglia having placodal cells give rise to gustatory fibers and in proportion to the size of the placodes and that all ganglia having epibranchial placodes give rise to gustatory fibers and particularly that a ganglion that is apparently exclusively placodal is also apparently exclusively gustatory, seems to warrant the assumption that placodal ganglia are special visceral ganglia.
48 F. L. LANDACRE
LITERATURE CITED
Beard, J. 1885-1886 The system of branchial sense organs and their associated ganglia in Ichthyopsida. A contribution to the ancestral history of the vertebrates. Quart. Jour. Micr. Sci. (n.s.), vol. 26, pp. 95-156.
Brookover, Charles 1910 The olfactory nerve, the nervus terminalis and the pre-optic sympathetic system in Amia calva. Jour. Comp. Neur., April.
CoGHiLL, G. E. 1902 The cranial nerves of Amblystoma tigrinum. Jour. Comp. Neur., vol. 12.
1906 The cranial nerves of Triton taeniatus. Jour. Comp. Neur., vol. 16.
Froriep, a. 1885 Ueber Anlagen von Sinnes-organs am Facialis, etc. Archiv fiir Anat. und Phys.
Herrick, C. J. 1899 The cranial and first spinal nerves of Menidia. A contribution upon the nerve components of the bony fishes. Jour. Comp. Neur., vol. 9, pp. 153-455.
1907 A note on the distribution of the IX nerve in author's paper ('07), p. 55.
Landacre, F.L. 1908 On the place of origin and method of distribution of taste buds in Ameiurus melas. Jour. Comp. Neur., vol. 18, no. 6.
1910 The origin of the cranial ganglia in Ameiurus. Jour. Comp. Neur., vol. 20.
Wilson, H. V. 1891 The embyrology of the sea bass (Serranus atrarius). Bull, of U. S. Fish Com., vol. 9, Washington.
WiJHE, J. W. VAN 1882 Uebcr die Mesodermsegments und liber die Entwickelung der Nerven des Selachier-Kopfes, Amsterdam.
ABBREVIATIONS
Aud. v., Auditory vesicle. Ec, Ectoderm
Aud., Auditory ganglion En., Endoderm
Br. IX, Branchial nerve of the IXth Ejpi., Epiphysis
5r. Xi, First branchial nerve of the Xth £•. P., Epibranchial placode (poster jBr.Xz, Second branchial nerve of the Xth lor extension)
J5r. Z3, Third branchialnerveoftheXth E. P. VII, Epibranchial placode of
Br. X4, Fourth branchial nerve of the the VII
Xth E. P. IX., Epibranchial placode of Br. A, Branchial artery the IX
Bv., Blood vessel E. P. Xi, First epibranchial placode of Bu., Ramus buccalis VII the X
D. L. VII, Dorso-lateral ganglion of E. P. X2, Second epibrancliial placode
the VII of the X
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS
49
E. P. X3, Third epibranchial placode
of the X E. P. Xi, Fourth epibranchial placode
of the X Gass., Gasserian ganglion Gen., Geniculate ganglion, general and
special visceral G. Cil., Ciliary ganglion. G. IX, Glossopharyngeus ganglion G. V. VII, General visceral portion
of the VII G. V. IX, General visceral portion of
the IX G. V. X, General visceral portion of
the X G. V. Xi, General visceral portion of
1st branchial of X G. V. X2, General visceral portion of
2nd branchial of X G. V. X3, General visceral portion of
3rd branchial portion of X G. V. X4, General visceral portion of
4th branchial of X Hyo., Hyomandibular cartilage Hyo. VII, Truncus hyomandibularis L. IX, Lateralis ganglion of the IX L. X., Lateralis ganglion of the X Mand. V, Truncus mandibularis V Max. V, Truncus maxillaris V Met., Metencephalon Mes., Mesencephalon N. Ill, Oculomotor nerve No., Notochord 0. VII, Ramus oticus VII Olf., Olfactory capsule
0-pt., Optic vesicle
O. Pro., Opthalmicus profundus nerve
0. S. v., Ramus opthalmicus superfi cialis V 0. S. VII, Ramus ophthalmicus super ficialis VII Pros., Prosencephalon Pro., Profundus ganglion Pal. VII, Ramus palatinus VII Pr. L. L., Primordia of lateral lines R. Aud., Root of auditory nerve R. VII, Root of facialis R. V, Root of trigeminus R. L. VII, Root of lateralis VII R. L. X, Root of lateralis X R. V. I, y/Root of visceralis VII R. V. X, Root of visceralis X St, IX, Ramus supratemporalis IX St. X, Ramus supratemporalis X Sup. L, Supra-orbital lateral line Sub. L, Sub-orbital lateral line S. V. VII, Special visceral ganglion
of VII S. V. IX, Special visceral ganglion of IX S. V. X, Special visceral ganglion of X
- S. V. Xi, Special visceral portion of 1st
branchial of X S. V. Xi, Special visceral portion of 2nd
branchial of X S. V. X3, Special visceral portion of 3rd
branchial of X S. V. Xi, Special visceral portion of 4th
branchial of X T. L. X, Truncus lateralis X
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 1
PLATE 1
A flat reconstruction of the brain, sense organs and sensory components of V, VII, VIII, IX and X cerebral ganglia of a 10 mm. embryo of Lepidosteus osseus.
General cutaneous ganglia are indicated by horizontal shading and this component is found at this stage in the profundus (trigeminus I) and the Gasserian ganglion (trigeminus II). The jugular ganglion of the X is not present at this stage; when it becomes organized it lies on the root of the X near the entrance of the root into the brain.
The special cutaneous ganglia are indicated by cross hatching and are found in the VII (dorso-lateral and ventro-lateral lateralis ganglia of the VII), in the VIII, IX and X.
General visceral ganglia are indicated by vertical lines and are found in the VII (geniculate), IX (petrosal), and X (nodosal).
The special visceral ganglia are indicated by stipple and are found in the VII, IX and X, there being only two of the four epibranchial ganglia of the X found at this stage. Aside from the hyomandibular nerve, all the nerve trunks are pure, i.e., contain only one component. The absence of the last two branchial ganglia and the lack of fusion in nerve trunks, which takes place later, are the chief differences between this embryo and older stages.
The scale at the side of the figure indicates the serial numbers of the sections from which the reconstruction was made.
50
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS
F. L. LANDACRE
PLATE 1
51
PLATE 2
A series of camera tracings of transverse sections of the head of Lepidosteus of 10 mm. length. The numbers following the number of the section indicate the level at which the section falls, as indicated on the scale over fig. 1. The sections are slightly diagonal, the right side of figure being further anterior.
Fig. 2 is taken at the level of the olfactory capsule and nerve.
Fig. 3 passes through the anterior portion of the Qptic vesicle and the epiphysis and dorsal sac.
Fig. 4 lies just posterior to the lens and passes through the anterior end of the profundus ganglion.
Fig. 5 passes through the third nerve, on right side of figure, and the posterior end of the profundus ganglion. The anterior end of the hypophysis is cut in this section.
Fig. 6 passes through the posterior end of the Gasserian on right side of figure and the anterior end of the lateral lobes of the medulla.
Fig. 7 passes through the root of the Gasserian ganglion on right side and the posterior end of the mesencephalon.
52
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS
F. L. LANDACRE
2 = V'^XSO
-Olf.
PLATE 2
5=//^x rf-a
OS. VII
--Pro.
-eu.vii
Max.V,
3-7<^X-iO.
6=/9y.\so.
-o.s.vij
Sup.L.
Sub.L. Bu.VII
A~/09.XS'O.
1-lf9.%S'0.
,-'--o.s.vil
-Bu.VII -Max.V.
53
PLATE 3
A continuation of figures of plate 2. All references are to the right side of figures.
Fig. 8 passes through middle of dorso-lateral VII and through the geniculate ganglion at the point where the placode was attached to the epidermis. The area blocked out in this figure lies in the middle of the series of figures on succeeding plate (fig. 18).
Fig. 9 passes through the posterior end of dorso-lateral VII and through the middle of ventro-lateral VII. The geniculate is cut posterior to the placodal ganglion.
Fig. 10 passes through the middle region of the auditory capsule and through the IX ganglion at the point of origin of its visceral trunk.
Fig. 11 passes through the epibranchial placode of the first branchial ganglion of X and the root of the lateralis X ganglion.
Fig. 12 passes through the middle of the lateralis X ganglion and through the visceral X just anterior to the epibranchial placode of the second branchial ganglion of X. The visceral root of X is cut in this section.
Fig. 13 passes through the posterior end of the lateralis X ganglion posterior to the posterior end of visceral X. The visceral root of X is cut in this section quite close to the medulla.
54
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS
F. L. LANDACRE
PLATE 3
]U 2.30.x JV.
Q^/OO.xrO.
12^2.vyAJO.
10=-2/'^12U2.
1 3 - 2 6/. X SO.
G.V.IX
-R.V.X
-LX
55
PLATE 4
Figs. 14 to 21 are a series of camera tracings of transverse sections of the 10 mm. embryo extending from the anterior end of the geniculate ganglion to the posterior end of the placodal portion of this ganglion. The anterior third of the ventro-lateral VII is included in the last two figures (20 and 21). Lateralis components are indicated by cross hatching, general visceral by vertical lines, and special visceral by stipple.
Fig. 18 corresponds to the area blocked out in fig. 8 of the preceding plate.
These figures were sketched from the same series as that from which the first reconstruction was made, fig. 1, and numbers of sections indicate position on scale of fig. 1. The figures are from consecutive sections. These figures show clearly the part the placode plays in the composition of the geniculate ganglion after the placode has become detached from the ectoderm.
Fig. 14 lies at the extreme anterior tip of the geniculate ganglion. See fig. 26 for detail of fig. 19, and fig. 27 for detail two sections posterior to fig. 21.
56
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS
F. L. LANDACRE
-Sup.L. -O.L.VII
PLATE 4
~ ~ Sub.L.
- 4- Hyo.
-Md.L.
D.L.VII
-s.v.vil
E.P.
\^-/s-^.x/oo.
l9=/<j-2.x/yo.
16-/i'^x /oo.
20^/6?.x/tJo.
D.L.VII
XJzz/oo.x/oo.
21=/6y.x/(?c/.
^ G.V.VI|-:,{
~:i,_No. V.L.VII ^C2
D.L.VII
E.P.
S.v.vil
PLATE 5
Figs. 22 to 25 from a 10.9 mm. embryo, are camera tracings to show the character of the placodal spur of the VII projecting laterally and caudally. Components are indicated as in preceding plate and in fig. 1. Lateralis or special cutaneous cross hatched; general visceral vertical lines; placodal or special visceral, stipple; figs 23, 24 and 25 are from consecutive sections. Two sections lie between figs. 22 and 23. The portion of this ganglionic complex shown in stipple is that which can be positively identified as placodal in origin. That more of the geniculate or general visceral should be shown as derived from the placode is possible, if the placodal cells have metamorphosed into ganglion cells. See fig. 28 for detail of fig. 23.
Fig. 26 shows the histological detail of the general visceral and placodal ganglia in fig. 19. The color differentiation due to size and density of cells is well shown in this figure. Length of embryo 10 mm.
Fig. 27 shows the detail of dorso-lateral, ventro-lateral and geniculate ganglia posterior to the placodal portion in a 10 mm. embryo. This section lies two sections posterior to that shown in fig. 21.
Fig. 28 shows the detail of the geniculate ganglion and the ventro-lateral ganglion in a 10.9 mm. embryo. This figure gives the histological detail of fig. 23 minus the dorso-latcral VII. Fig. 2S should be compared with fig. 26, since they are taken through approximately the same region of the geniculate ganglion of embryos differing nearly 1 mm. in length. The constancy in appearance of the placodal ganglion is striking.
58
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS
F. L. LANDACRE
PLATE S
G.V.VI
2Q/.36-0.
h
^vsvvil
^i^^.
27 X3cr^ . „,
U^
a
05 ^0 e) o,-^
>)^>^
%1
-GVVII
^0
0%^0 '-^^91
DO
®0.^_
vV.L.VII
28 X5J-0
P
o
-G.V.VII
■VII
s.v.VIl
PLATE 6
Fig. 29 from a 12.4 mm. embryo, is taken from approximately the same position in the VII ganglionic complex as fig. 25, which is from a 10.9 mm. embryo. There are no placodal cells present in this section except the caudally projecting spur. This is soon incorporated into the geniculate ganglion. The close resemblance histologically between the dorso-lateral and the geniculate, and the distinct character of the ventro-lateral which are so noticeable in this figure, can be detected in all earlier stages.
Fig. 30 is taken from the same embryo (12.4 mm.) as that from which fig. 29 was taken and lies five sections anterior to fig. 29. Only the anterior tip of the ventro-lateral ganglion shows and the dorso-lateral has been omitted on account of its size. The placodal ganglion projects somewhat from the ventro-lateral surface of the geniculate.
Fig. 31 shows the same relations in a 13.5 mm. embryo. The placodal ganglion is almost completely incorporated into the geniculate. The distinction shown here between unaltered placodal cells and the normal ganglion cells of the geniculate is fairly representative for all later stages in which placodal cells can be detected.
Fig. 32 shows the detail of the epibranchial placode of the VII in a 9.5 mm. embryo and illustrates the relation of the placode to the ectoderm above and below its point of attachment. This figure corresponds to the middle of the placode shown in fig. 33.
Fig. 33 is a sketch of a wax reconstruction of the epibranchial placode of VII and associated structures in the ectoderm and endoderm. The model rests on its anterior surface and is seen from the ventral surface. The ectoderm with its attached epibranchial placode is detached from the endoderm and that portion of the ectoderm lying anterior to the placode. The hyoid gill pocket lies to the right and is closely fused with the ectoderm back to the point of origin of the placode. If the two portions of the model are placed together it will be seen that the anterior surface of the epibranchial placode rests upon the posterior surface of that portion of the hyoid gill pocket that comes into contact with the ectoderm. The length of the embryo from which the model was reconstructed was 9.7 mm.
m
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS
F. L. LANDACRE
PLATE 6
29\^-"'
4o ^Oc3A>
-D.L.VII
,9 Vo 1SC? ■
o
m
^^p%9
0^
^V.L.VII
32x3^(7
30 xB^c?
G.V.VII
\s.v.vil
V.L.VIi
G.V.Vll
e.v.vil- -^-C
^?^i^
0~ f\^
fTs Ooi'O,
■©
O
© o < j-j o o j>i
G
- CCCo-<^^
■C^
•s.v.vil
33
Pr.LL.
,'GV IX
— - En.
61
PLATE 7
Fig. 34 from an 82 hr. embryo is taken through the posterior portion of the thickening of the ectoderm at the point where the endoderm of the pharyngeal gil 1 pocket joins it. The ectoderm is easily distinguished by its color.
Fig. 35 from an 82 hr. embryo is taken through the thickening in the epidermis just posterior to the hyoid gill pocket and is presumably the anterior extension of the preauditory placode and, although it is not detached from the auditory vesicle, it shows none of the histological characters of the preauditory placode. Fig. 35 lies three sections posterior to fig. 34.
Fig. 36 from a 94 hr. embryo, is taken at the extreme posterior limit of the contact of the pharyngeal gill pocket with the ectoderm. The nuclei of the ectoderm are closely packed and the cell walls are indefinite or absent, showing distinctly that it is related to the epibranchial placode rather than to the preauditory placode.
Fig. 37 from a 94 hr. embryo is taken just posterior to the contact of the hyoid gill pocket with the ectoderm and shows the proliferation of cells to form the epibranchial placode. Fig. 37 is the next section posterior to 36.
Figs. 36 and 37 show the absence of any primordium of the lateral lines in the region of the placode up to this age.
Fig. 38 from a 7.3 mm. embryo is taken at the posterior limit of the contact of the hyoid gill pocket with the endoderm. In addition to the ectodermic gill thickening there is a dorsal thickening (primordium of lateral line).
Fig. 39 from a 7.3 mm. embryo is taken just posterior (two sections back of fig. 38) to the contact of the hyoid gill pocket with the ectoderm. It shows three thickenings ; most dorsal, the primordium of the lateral line ; most ventral the probable remnant of the preauditory placode. The middle thickening is the epibranchial.
62
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS
F. L. LANDACRE
PLATE 7
Ec.
34 X3ro
5^,4iM^v
■^0mm.-9
Ec
36 -x3i'o.
J
^^ ; ^i^
- )J?'3^
t)x
<?
Q
En-
•9 Ec. 37 y 3^0.
Q
3"^
"5) :i i ,V;
(5
fSS-^M
38 xsi-c?
Ec.-
39 x3i-o.
-Pr L. L.
^En.
^^
63
PLATE 8
Fig. 40 is from a 7.3 mm. embryo. The section passes through the posterior extension of the epibranchial placode of VII and the posterior extension of the primordium of the sensory line lying dorsal to it. This section contains the anterior end of the geniculate ganglion and lies four sections posterior to fig. 39.
Fig. 41 from an 8 mm. embryo, passes through the extreme posterior portion of the contact of hyoid gill pocket with the ectoderm. It shows in addition to the differentiation between ectoderm and endoderm the fact that the geniculate ganglion sometimes extends forward over the phyarngeal gill pocket. The primordium of the sensory line lies well dorsal to the ectodermic gill thickening.
Fig. 42 from an 8 mm. embryo, shows the first section posterior to the point where the hyoid gill pocket withdraws from the ectoderm. The epibranchial placode is cut through its anterior end. The small mass of cells lying between placode, endoderm, and geniculate ganglion may belong either to the placode or to the ganglion since the ganglion has a rather indefinite outline.
Fig. 43 from an 8.3 mm. embryo, shows the maximum size of the placode at this age. The indefinite outline of the geniculate ganglion at this stage renders the line of separation between the placode and the geniculate ganglion difficult of determination.
64
THE EPIBRANCHTAL GANGLIA OF LEPIDOSTEUS
F. L. LANDACRE
40 y^3 5-o
Pr.L. L.
PLATE 8
,E.P.VII
t)C
,Gen.
- ?v ••-7 ' J <■ i'?)jr^
Ec
05ot
- o oocn
41 x3:yo
-Pr.L. L.
EPVII
Gen.
COO
42x3r(;
EPVII
Gen.
DLVJI
--V^r
43 ^3so
O3
<&
a
.0
■CO c
^^o'loOo-.-Ec.
•^o
'EPVII
00^0
^^0^0
o ® o
O .;
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 1
65
PLATE 9
Fig. 44 from an 8.8 mm. embryo shows the earliest trace of cells in the IX that would ordinarily be identified as placode. Succeeding series do not show it to be continuous and it differs from other placodes in having the ectodermic shelf extend mesially to the placodal cells.
Fig. 45 from a 9.7 mm. embryo shows, in the IX, the earliest trace of the placode that can be followed continuously in later series up to the time of its detachment.
Fig. 46 from a 10 mm. embryo shows the 'comma' stage of IX immediately after or during its detachment from the epidermis. The placode is not sharply differentiated from the general visceral, but includes at least all of the ventro-laterally projecting mass. The whole ganglion rests upon the ectodermic shelf.
Fig. 47 from a 12.4 mm. embryo passes through the anterior end of the placodal ' mass of cells of IX and is almost surrounded by the general visceral cells.
Fig. 48 from a 12.4 mm. embryo passes through the point where the lateral spur of placodal cells is present and the remainder of the placodal cells are only partially incorporated and occupy the ventral side of the ganglion. Fig. 48 lies three sections back of fig. 47.
Fig. 49 from a 10 mm. embryo shows the early stage of the epibranchial placode of the first branchial ganglion of X still attached to the ectoderm.
66
THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS
F. L. LAND ACRE
PLATE 9
.O,
-^^
'^Z
o
o
. -(3
3
o^
EPIX
_^
46 ^'^^"'^
CS
Ec
- ,<^i
Ci
Hi:
o
/>
©
Q
.
49 K3S0
O
>5
Vr.^ 3 C?^
^^^o^
EP X-1
o
^^ 5^/c.^ ^,; -'^r ^a o ^. " -svix / o-p ^^^ ■.% Wi Ec ^e C 67 r-T-n Q 47X3:ro j^^^^ AudV BV 13^ 0-0 ^i^'d-o <5) ?. PLATE 10 Fig. 50 from a 11.5 mm. embryo is taken through the 'comma' stage of the placode of the first branchial ganglion of X and shows the relation assumed by the placodal and general visceral cells in a ganglion where they are approximately equal in number. Fig. 51 from a 10 mm. embryo shows an early stage of the epibranchial placode of the second branchial ganglion of the X at a stage where it is still attached to the ectoderm. Fig. 52 from a 10.9 mm. embryo shows a late stage in the second epibranchial ganglion of X. The incorporation of placodal cells is not complete, there being a ventro-lateral spur of placodal cells and, contrary to the usual rule, the placodal cells lie chiefly on the lateral portion of the general visceral ganglion. Fig. 53 from a 10.9 mm. embryo shows an early stage before detachment of the epibranchial placode of the third branchial ganglion. Fig. 54 from a 11.5 mm. shows the process of incorporation of the third epibranchial placode into the ganglion of the X. The lateral spur is still present. Fig. 55 from a 12.9 mm. embryo shows, an early stage in the formation of the fourth epibranchial placode of the X. The general visceral cells are so numerous that the relation seems to be one of contact only but later series show that there is an actual contribution by the placode of the ganglion. 68 THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS F. L. LANDACRE PLATE 10 50 >. 3 5-0 f J' ;i ^ xa Q "^"^ -^<., IGJS' ^o^®o%^ G>:^ I; ^ ^P^^ %^ Ec. GV X ^ o ^S. ^<^^^^^l ,^0 EPX-3 o \o- 0-^O^C^ Ec ,d*f^i 51 x3ro ^ IP ^ ^^p iD^ < o &2§' 52 X5 5-0 i^^^ EP X-=» Vs CH. ^0 .^ ._Ec. '^O'^ " ^ ^0 ,:% 0% c)« o^^O ^rpe.^ -^ © ^"^^ Ec G.V X-3-^ ^ i?~af^ B.V 54 xsj"!? Q^C? s o o^t. o O O s^^vQ O n o ^ j-^ -s-' cv^ p"^s V. x-3 b5^3so © o ^ ^ <3 o <S) re (^"i fS Or=^ ^^/-^' 69 A COMPARISON OF THE EUROPEAN NORWAY AND ALBINO RATS (MUS NORVEGICUS AND MUS NORVEGICUS ALBINUS) WITH THOSE OF NORTH AMERICA IN RESPECT TO THE WEIGHT OF THE CENTRAL NERVOUS SYSTEM AND TO CRANIAL CAPACITY HENRY H. DONALDSON The Wistar Institute of Anatomy and Biology FIVE FIGURES In a paper recently published (Donaldson and Hatai, '11) the fact that the domesticated albino rat (Mus norvegicus albinus) of our laboratory colony has a relatively smaller central nervous system than the wild Norway (Mus norvegicus) from which it is derived, has been presented and examined in some detail. This difference between the two forms has been known to us for several years and ever since it was first appreciated we have been in search of a satisfactory explanation for it. In the paper just cited, the conclusion is reached that this difference represents one effect of domestication on the albino rat, but in order to justify this conclusion, it will be necessary not only to analyse domestication into its main factors, but also to test other explanatory suggestions which have been made. One such suggestion is to the effect that the small relative weight of the central nervous system in the domesticated Albino is due to the fact that the Albino has been derived from a strain of the wild Norway in which the central nervous system was also relatively small. It was to test this suggestion that the present study has been made. At the same time we recognize that this question represents one aspect only of the larger problem of the possible variations 71 72 HENRY H. DONALDSON which the Norway rat has undergone in its migration across Europe and over seas to the Americas. From our experience with the wild Norways of North America, as found in Chicago and Philadelphia, there is no reason to think that such an established strain exists in the United States, although there appear to be slight differences characteristic for the rats from different stations, and in one instance the rats from a restricted locality near Philadelphia showed a brain weight decidedly lower than that of our standard series. We do not look on this latter group however as representing an established strain. It was thought possible nevertheless that such a strain might be found in western Europe and I decided therefore in the summer of 1909 to test the matter by collecting both Norway and albino rats from Vienna, Paris and London in order to compare these in respect to their central nervous systems with specimens of both forms as observed in Philadelphia. Historically, nothing is known of the albino variety of the Norway rat, not even whether the Albinos found in Europe and those in North America have had a common origin. Concerning the wild Norway rat, we are a trifle better informed. Mus norvegicus is reported by Pallas to have entered Europe by way of southern Russia about the beginning of the eighteenth century. It arrived in England, by ships, about 1728-1729 and in Paris about 1758, but of its first arrival in Vienna, I have found no mention. The date of its arrival on the eastern seaboard of the United States was about 1775 (Lantz, '09). Thus the wild Norway rat has been in Europe for nearly two hundred years, and in the eastern United States for about a hundred and thirty-five years. It seems most probable that the albino variety has been established since the appearance of the wild Norway rat in Europe. For the opportunity to make these studies on the rat at the several European stations, I was indebted to the courtesy of colleagues in each city, and it is a pleasure to present here my thanks to all of them for their unfailing kindness and interest. At Vienna, Professor Obersteiner obtained for me a table in BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 73 the Physiological Institute directed by Professor v. Exner. Through Dr. Przibram, Director of the Biologische Versuchsanstalt, arrangements were made to get Norway rats and ultimately Dr. Przibram, beside presenting me with some of his own Albinos, kindly allowed his assistant. Dr. Megusar, to make for me the collection and first measurements of the animals needed to complete the Vienna series. My thanks are specially due to Dr. Megusar for the precision and care with which this work was done. In Paris, Professor Lapicque obtained for me a table in the Physiological Laboratory at the Sorbonne, and in every way aided my plans. Finally, in London, Sir Victor Horsley courteously allowed me to work in his own laboratory and through his assistants arranged for the supply of animals. It may be noted in passing that rats in these several cities are most readily obtained through local dog fanciers who usually control a supply used for the higher education of their terriers. Norway rats were hard to get in Vienna. Possibly the war of extermination waged against them about 1898, when public interest was aroused by a laboratory outbreak of plague, has served to check their increase. In Paris the rats were easier to obtain, but bore evidence of having been caught in rather unsavory surroundings. In London they were very numerous. I was offered a thousand in three days, and moreover Mus rattus alexandrinus and Mus rattus, the old English black rat, were also to be had — both kinds in large numbers. The general plan of this investigation was the following: To collect at each of the three foreign cities about one hundred Norway rats — and a smaller number of Albinos; to record the body weight and body length of each individual, and in a few cases to remove and weigh the central nervous system on the spot. In the majority of cases however, it was planned to preserve the heads only. Later the skulls were to be prepared in this laboratory, the cranial capacity determined and the data from the several series 74 HENRY H. DONALDSON as thus obtained, used as a basis for determining the relative weight of the brain. Moreover, corresponding series of animals from Philadelphia were to be prepared by a like technique and these data in turn used as standards with which to compare the European records. This plan was carried out, and the results furnish the material for the discussion which follows. The constitution of the several series of specimens is shown in tables 1 to 11 inclusive. These tables give by series the number of individuals and the range in body weight for each sex separately. TABLE 1 Mus norvegicus from Vienna NUMBER RANGE IN BODY WEIGHT Males 38 55 grams 78^00 Females 68-354 TABLE 2 Mus norvegicus albinus from Vienna NUMBER RANGE IN BODY WEIGHT Males . . ... 4 6 grams 180-292 Females 142-204 TABLE 3 Mtis norvegicus from Paris NUMBER RANGE IN BODY WEIGHT Males 50 46 (/rama 64-391 Females . 86-389 BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 75 Mus norvegicus from Paris. Used for direct determination of the weight of the central nervous system NTjMBER RANGE IN BODY WEIGHT Males 7 2 grams 183-328 Females 154-234 TABLE 5 Mus norvegicus albinus from, Paris NUMBER RANGE IN BODT WEIGHT Males 8 2 grams 86-203 Females 94-109 TABLE 6 Mus norvegicus from London NUMBER RANGE IN BODY WEIGHT Males 51 45 grams 72-385 Females 88-382 TABLE 7 Mus norvegicus from London. Used for the direct determination of the weight of the central nervous system Males Females. grams 157-305 173-215 TABLE 8 Mus norvegicus albinus from London NUMBER RANGE IN BODY WEIGHT Males • 5 5 grams 106-286 Females 150-250 76 HENRY H. DONALDSON TABLE 9 Mus norvegicus from Philadelphia NUMBER RANGE IN BODY WEIGHT Males 49 46 grams 104-533 Females 75-457 TABLE 10 Mus norvegicus albinus from Philadelphia. Prepared in 1910-11 NUMBER RANGE IN BODY WEIGHT ^lales 9 11 grams 101-194 Females 72-124 TABLE 11 Mus norvegicus albinus from Philadelphia and 1907 by Dr. Hatai Chicago. Material prepared in NUMBER RANGE IN BODY WEIGHT Males 41 35 grams 112-292 Females 108-253 An examination of the data for the four longer series — namely those for the wild Norways — used in the determination of cranial capacity (tables 1, 3, 6 and 9) suggests several comments. In collecting these series no selection by either size or sex was made by me, and yet the proportion of the sexes is rather similar in all four. In the three European series, the range in body weight is also similar, while distinctly heavier rats are found in the Philadelphia series. It may be remarked that in this latter case we received every animal caught, while it is just possible that in the case of some of the European series, the dealers reserved the very largest animals for their own use, and in this way modified the range in body weight. However that may be, the data as they stand show that the several series were taken from rat populations which were similar in their general composition. BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 77 TECHNIQUE In all cases the rats were brought alive to the laboratory, killed with chloroform, weighed and the body length taken (see Donaldson, '09). Then, either the central nervous system was removed and weighed, according to the usual technique (Donaldson and Hatai, '11) or the head cut off. This latter was marked with a numbered metal tag and preserved in 60 per cent alcohol, pending the preparation of the skull. As all the series were treated in the same manner, the effects of the 60 per cent alcohol in modifying the capacity of the cranium should be similar, provided of course that the composition of the skull bones was also the same. The skulls were cleaned by immersion for from 5 to 6 hours at a temperature of 90° C. in 100 cc. of a 2 per cent watery solution of commercial 'gold dust washing powder.'^ The very young skulls required less time and a half strength solution. The softened tissues were removed with a bone scraper. The skull was then marked with water proof ink, dried in the air, and the foramina at the base plugged with a minimal quantity of universal cement to prevent the escape of the shot later used for determining the cranial capacity. To determine the capacity of the dried cranium- it was filled with new number eleven shot. These shot are 0.06 of an inch in diameter and weigh individually from 0.0203 to 0.0215 grams and therefore run from 47 to 49 to the gram, with a mean of 48. In filling the cranium the following method was used: The cranium was held vertically between the thumb and forefinger of the left hand with the ventral side towards the observer. The shot was poured from a small aluminum beaker into the cranium through the foramen magnum until it was nearly filled, then transferring the cranium to the right hand, and holding it vertically between the thumb and middle finger with the index finger closing ^ 'Gold dust washing powder' consists of about 45 per cent sodium carbonate, 30 per cent soap powder and 25 per cent water. - Departing from the strict anatomical nomenclature, and following the usage of the anthropologists, we shall here employ the term "cranium" for the skull without the mandible (see Cunningham, '09, p. 103, note 1). 78 HENRY H. DONALDSON the foramen magnum, the right hand was gently struck three times against the left. This was done to pack any shot which might have been caught on irregularities within the cranium. ^^ The cranium was then transferred to the left hand again and held as before while more shot were poured in. These were packed with a small spatula and finally pressed down with the forefinger of the right hand. The filling was such that the shot was slightly heaped in the center of the foramen so as to rise a httle above the level of its edge. When thus filled, each cranium was placed vertically, nose down, in a small weighing bottle, so that no shot should be lost through accidental jarring. The filled cranium was next weighed to the tenth of a milligram and the weight of the shot computed by subtracting from the weight of the filled cranium the weight of the empty cranium as previously determined. The cranium was then emptied and again filled and weighed, and if the two weights of the shot were within one per cent of one another, they were deemed satisfactory. In 84 per cent of the cases tw^o weighings only were necessary. When the discrepancy was greater than 1 per cent in the first instance, and more than two weighings were required, the two determinations in closest agreement were selected for averaging, and the number thus obtained was that recorded. In this connection it may be noted that in the nine series of crania measured in the course of this investigation, the mean difference between the two weighings of shot which were used as the basis for the averages, was 0.6 per cent. This corresponds to a mean difference of from three to five shot according to the total weight of the shot required to fill the cranium. 3 As serving to illustrate the pitfalls besetting the determination of cranial capacity by the use of shot, I may call attention to the fact that when a container has been filled, it does not always follow that any disturbance of the contained shot will decrease its volume. For example : if a glass measuring cylinder graduauated to hold 10 cc. and having an internal diameter of 1 cm. is exactly filled to the upper limit of the graduation with number 11 shot, poured into it in a steady stream, so that the filling rocjuiros about fifteen seconds, and then the mouth of the cylinder is closed with the thumb and the cylinder once inverted, the shot having a run within the cylinder of about .5 cm., it is found that the volume of the shot is increased by this treatment about 0.5 co. or 5 per cent. If the cylinder be now gently tapped on the bottom (;ight or t<Mi times, the volume of the shut again diminishes to its original value. BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 79 This technique is essentially that which was used by Hatai ('07) but has been given here in detail because in the determination of cranial capacities, concordant results can be obtained only by the strictest adherence to a uniform procedure. The various measurements made by the foregoing methods have been recorded and tabulated in detail and the individual records are on file at the Wistar Institute where they are at the service of other investigators. In the presentation which follows however, we shall use only mean values, grouping the records for each series by mean body weights within weight groups differing by 50 grams. The smallest weight group includes the individuals between 51 to 100 grams in body weight, and the largest those between 351 to 400 grams. The higher body weights appearing in the Philadelphia Norway series have not been considered because there are no European records with which to compare them. BODY FORM Before taking up the records touching the central nervous system, it is important to know whether the several series to be examined are composed of animals having a like body form. The most general test for likeness in form is the relation of body length to body weight. The data for such a test are contained in tables 12 and 13. For our present purpose therefore we select from these tables the records giving the mean body weights and mean body lengths for each weight group of each series. In chart 1 these data for body length both for the Norways and Albinos are entered in relation to the standard curves for body length based on Philadelphia material (Donaldson '09 and Donaldson and Hatai, '11). A study of chart 1 shows that the European series of both forms agree fairly with the standard records as represented by the continuous curves in the chart. The records for the European Norways run somewhat below the standard. This is especially noticeable in the case of the Vienna and Paris series. The records for the European Albinos agree very closely with the standard curve based on the Philadelphia Albinos. On the whole, the accordance between the 80 HENRY H. DONALDSON 250 2401 230 220 210 200 190 180 170 160 150 140 130 BODY LENGTH mm. STANDARD CURVE NORWAY STANDARD CURVE ALBINO CHART BODY WEIGHT gms. 250 240 230 220 210 200 190 180 170 160 150 140 130 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 Chart 1, giving the body length in millimeters for each of the three European Norway series separately in relation to the standard curve for the body length of the Philadelphia Norwaj^s. Also giving the body length for the three European albino series combined, in relation to the standard curve for the body length of the Philadelphia Albinos. Norways: = Paris series, 13 = London series, V = Vienna series. Albinos: X = European series (combined). European series and the standards is close. Hence we conclude that in body form, the European Norways are similar to one another and to the Philadelphia standard, and that the same relations are true for the European and Philadelphia Albinos. Since the completion of this manuscript, a paper by Chisolm ('11) has appeared in which he compares the body length of tame albino and piebald rats of London with those of the Philadelphia Albinos as given by me in an earlier paper (Donaldson, '09). Chisolm's measurements agree with mine very well up to about 100 grams of body weight and from there on fall steadily below the Philadelphia records with a maximum deficiency of about 5 per cent. It seems probable however that this difference is mainly due to the difference in the method of taking the body length. BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 81 TABLE 12 Giving for each body weight group of Mus norvegicus the mean values for all the individuals from each of the four stations. Below each weight group is also given the mean for the European series alone. Records from Philadelphia = A; Paris = P; London = L; Vienna =V NUMBER or CASES BY SEX MEAN ■WEIGHT GROUP SERIES MEAN BODl MEAN BODl CRANIAL WEIGHT LENGTH CAPACITY M. F. , grama mm. cc. A
- 1
74.9
157
1.575
51-100 <
p
1
2
79.3
142
1.533
L
3
4
87.8
156
1.509
, V
3
4
80.6
148
1.567
Mean of European series
82.5
149
1.536
A
2
3
128.2
179
1.828
101-150 <
P
10
7
130.1
177
1.795
L
5
7
126.1
179
1.653
V
4
5
126.0
178
1.694
Mean of European series
127.4
178
1.714
A
5
11
179.5
194
1.897
151-200
P
3
10
173.8
195
1.894
! L
8
7
177.1
199
1.898
V
8
20
171.4
193
1.788
Mean of European series
174.1
196
1.860
A
11
6
226.2
214
2.000
201-250 <
P
11
9
221.5
209
2.002
L
14
8
224.7
214
1.980
V
9
14
223.9
211
1.936
Mean of European series
223.4
282.9
211
225
1.972
A
5
8
2.131
251-300 <
P
15
10
277.8
224
2.129
L
12
13
272.3
224
2.053
V
8
7
261.7
221
1.978
Mean of European series
270 6
223
2.053
A
4
13
326.2
237
2.210
301-350 <
P
7
5
322.2
234
2.205
L
8
5
320.7
234
2.090
V
2
4
322.7
235
2.154
Mean of European series
321 9
234
2 149
A
13
2
377.7
246
2.285
351^00 <
P
3
3
377.6
238
2.248
L
3
1
375.3
246
2.318
V
4
1
377.9
245
2 225
Mean of European series
377
243
1
2 264
1
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22 , NO. 1
82
HENRY H. DONALDSON
TABLE 13
Giving for each body weight gr-oup of Mus norvegicus albinus the mean values for all
the individuals from each of the four stations. Below each weight group is also
given the mean for the European series, so far as represented in the group.
Records from Philadelphia = A; Paris = P; London = L; Vienna = V
WEIGHT GROUP
SERIES
NUMB
CASES
M.
ER OF
BY SEX
F.
MEAN BODT
WEIGHT
MEAN BODT
LENGTH
MEAN
CRANIAL
CAPACITY
grams
mm.
CC.
A
5
87.8
157
1.364
51-100 <
P
L
V
1
1
90.0
158
1.443
Paris series
90
127.3
158
173
1 443
A
11
15
1.524
101-150 <
P
L
5
1
1
1
117.6
128.0
175
171
1.560
1.494
V
2
145.5
174
1.497
Mean of European series
130 4
174
1 517
A
19
23
174.2
193
1.661
151-200 <
P
L
1
2
173.0
184.0
194
196
1.671
1.646
.
V
1
3
160.2
184
1.638
172 4
191
1 652
c
A
13
2
218.6
1.743
201-250 1
P
L
1
1
1
203.0
234.7
203
209
1.822
1.758
V
1
1
213.5
199
1.704
Mean of Eurouean series
217.1
204
1 761
^ ,
A
7
1
275.9
1.768
251-300 I
P
L
3
1
276.6
218
1.805
V
2
289.4
222
1.916
Mean of London and Vienna
series .
283
220
1 860
(.'hisolni used the posterior inargin of the symphysis pubis,
while I used the anus, as the caudal limit of the measurement and
thus my measurements must give slightly greater values than were
found by him. When correction is made for this difference in
method, the two series of records agree nicely and give a welcome
BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 83
confirmation of the statements just made concerning the similarity of the albinos on the two sides of the Atlantic.
In this case of body length, as in that of the other data on the
weight of the brain and spinal cord and on cranial capacity, to be
presented later, the records are for the two sexes combined, since
the differences according to sex are so small as to be negligible for
the present investigation (Donaldson and Hatai, '11).
WEIGHT OF THE CENTRAL NERVOUS SYSTEM
The establishment among the several series of the similarity in
body form clears the way for the study of the weight of the central
nervous system in these same series. The method of direct
weighing is the simplest and, as it has turned out, the most satisfactory method of attacking the problem before us. Had I to
repeat this investigation I should make only direct determinations
on the weight of the brain and spinal cord and omit those on
cranial capacity, but when the investigation was begun, it was
thought that the longer series of cranial capacity determinations
would be more valuable than a shorter series of direct weighings,
which require withal more time to make ; and my time was limited.
Nevertheless I had planned from the first to make direct weighings
of the central nervous system for very short series of the Norways
at each of the European stations. This was not done at Vienna
because specimens for the purpose could not be obtained during
the period of my stay there, but it was done for both the Paris
and the London Norways. It is these latter records which are
now to be considered. The data are given in tables 14 and 15.
When these data for the weight of the brain and the weight of
the spinal cord are entered in relation to the corresponding standard curves for brain weight based on body weight (Donaldson and
Hatai, '11) as given in chart 2, it is plain that both the European
series closely agree with the respective standards for brain and
spinal cord. The mean percentage deviation of the values as
observed, from those of the standards, are given in table 16, A.
For comparison and control we have also given in table 16, B,
the mean percentage deviation of the values as observed from
84
HENRY H. DONALDSON
values for the brain weight when based on the body length (Donaldson and Hatai, '11, tables 5 and 8). It will be noted that
the two series of results agree very well.
BRAIN WEIGHT
2.4
2.3
2.2
2.1
2.0
1.9
1.81
gms.
CHART 2.
STANDARD CURVE
NORWAY
STANDARD CURVE
ALBINO
2.4
2.3
2.2
2.1
2.0
1.9
SPINAL CORD WEIGHT
0.9
0.8
0.7
0.6
0.5
gms.
STANDARD CURVE
NORWAY
STANDARD CURVE
ALBINO
BODY WEIGHT gms.
-10.9
0.8
0.7
0.6
0.5
'60 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330
Chart 2, brain and cord weight of Paris and of London Mus norvegicus, entered
in relation to the respective standard curves for the Philadelphia data. For further control, the corresponding standard curves for the Philadelphia Albinos are
also given on the chart. O = Paris series, n = London series.
BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 85
TABLE 14
Mus norvegicus, Paris. Weight of brain and spinal cord
WEIGHT GROUP
NUMBER OF CASES BY
SEX
BODY
WEIGHT
BODY
LENGTH
WEIGHT OF
M.
F.
Brain
Spinal cord
151-200
1
3
1
2
1
1
grams
168.6
237.7
293.0
317.0
mm.
191
219
230
227
grams
2 1410
2.2028
2.3514
2.2733
grams
0.6045
201-250
0.6838
251-300
0.8630*
301-350
0.7785
TABLE 15
Mus norvegicus, London. Weight of brain and spinal cord
WEIGHT GROUP
NUMBER OF C.\SE8 BY
SEX
BODY
WEIGHT
BODY
LENGTH
WEIGHT OF
M.
F.
Brain 1 Spinal cord
151-200
201-250
251-300
301-350
3
1
1
1
3
grams
173.0
208.5
305.0
mm.
197
210
237
grams grams
2.0959 0.5815
2.1404 0.6328
2.2440 0.8031
- As this record for the spinal cord, which is correct, is also exceptional and is
based on a single case only, the record is not used in computing the percentage
deviations given in table 16.
TABLE 16
Mus norvegicus. Mean percentage deviation of the weight of brain and spinal cord
in the Paris and London series from the standard values for the Philadelphia
Norways
A. Comparison on the basis of body weight, as given in table 2
SERIES
MEAN PERCENTAGE DEVIATION
Brain
Spinal cord
Paris
+2.0
0.0
+2.7
London
+ 1.4
Average
+1.0
■ +2.0
B. Comparison on the basis of body length
Paris
+2.9
-0.2
+4.5
London
+0 9
Average
+1.4
+2.7
Average of both A and B
+1.2
. +2.4
86 HENRY H. DONALDSON
The average of the deviations as given in tables 16, A and 16,
B, is the figure used in the subsequent discussion.
According to these determinations, it is plain that both the
Paris and London Norways have central nervous systems (brain
and spinal cord) slightly heavier than that of the standard Philadelphia Norways. The deviations of the European forms from
the standard are so small however, even in the case of the Paris
series, that they are probably not significant. It is possible to
conclude therefore that the Paris and London rats do not have
central nervous systems of less relative weight than those found in
the Philadelphia Norways, while as the records stand, the relative
weight is really slightly higher. Although, as has been explained,
the corresponding data for the Vienna Norways are lacking, we
shall see further on that the true cranial capacity of the Vienna
Norways is compatible with a brain weight about equal to that of
the Philadelphia series or a trifle below it — but probably not
deviating to any significant degree.
Although the data for the percentage of water in the brain and
spinal cord are not presented here because the determinations
could not be made abroad with all the desired precautions, yet the
data as they stand agree well with those for the American Norway
as previously determined (Donaldson and Hatai, '11). In this
respect then the European and American Norways are again in
agreement.
The foregoing determinations are highly important for the
control and interpretation of the data on cranial capacity since
these latter, as we shall see, cannot be taken at their face value,
but must be corrected for shrinkage, which varies not only according to age, but also according to other less evident conditions.
The characters of these crania, so far as they are indicated by
weight, have been discussed elsewhere (Donaldson '12).
CRANIAL CAPACITY
In determining the cranial capacity by the methods given earlier
we obtain in the first instance the weight of the shot necessary to
fill the cranium. It was found that one cubic centimeter of the
BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 87
shot used weighed 6.354 grams ± 0.020, hence the observed
weight in grams is transformed into volumes in cubic centimeters
by dividing the weight of the shot by 6.354. In tables 12 and 13
the data on the cranial capacity in cubic centimeters are presented
for each one of the entries.
Taking the entries in table 12, which refer to the wild Norways,
we wish in the first instance to learn how the cranial capacities
of the several European series are related to that of the Phila
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1,7
1.6
1,5
CRANIAL CAPACITY OF
NORWAY RATS
c,c.
PHILADELPHIA
RECORDS
CHART 3,
l2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
BODY WEIGHT gms.
60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380
Chart 3, showing the cranial capacity in cubic centimeters for the four Norway
series. The values for the Philadelphia series are represented by a curve computed from formula (1). The values for the European series are entered separately. O = Paris series, D = London series, V = Vienna series.
delphia series taken as a standard. To show this, the European
data have been plotted by groups on chart 3, while the Philadelphia records are represented by a continuous line showing the
computed values. For the formula for this line, I am indebted
to Dr. Hatai.
The relation between the computed and the observed values in
the Philadelphia series is close. Except for the second entry
at 128.2 grams, which entry is a trifle high, the observed data for
the cranial capacity of the Philadelphia Norways show an orderly
88 HENRY H. DONALDSON
increase. Assuming then that the terminal values are correct,
that the second entry is aberrant and that the intermediate values
are approximately normal, Dr. Hatai determined the formula
for the curve which fits the observations. This formula is as
follows :
ij = 0.00105 X + 0.548 log x + 0.476 (1)
where x equals the body weight and y the cranial capacity in cubic
centimeters.
Examination of chart 3 shows at once that the three series of
the European records do not run exactly with the line representing
the Philadelphia series. Inspection shows that the order of the
TABLE 17
Mus norvegicus. Showing the mean percentage deviation in cranial capacity for
each of the three European Norway series from the Philadelphia series taken as a
standard
SERIES
MEAN PERCENTAGE
DEVIATION
Paris
-0.4
London
-2.5
Vienna ■
-3.3
Average
-2.1
mean values from highest to lowest is Philadelphia, Paris, London
and Vienna. If then we compute the mean deviation from the
Philadelphia records for each of the European series given on the
chart, we obtain the values entered in table 17.
As table 17 shows, the average of the mean deviations for the
cranial capacity of the European Norway series combined is —2.1
per cent. It thus appears that all the European series for the
Norway rat exhibit a smaller cranial capacity than the Philadelphia series and that the most marked deviation occurs in the case
of the London and Vienna series where the deficiency is 2.5 and
3.3 per cent respectively.
For the Albinos, the Philadelphia series are also taken as the
standard. The curve is represented by the continuous line in
BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 89
chart 4. This is calculated from formula (2). The observed
value for the smallest weight group of the Philadelphia series
was considered normal (see table 13) but that for the largest
weight group was taken midway between the value for the Vienna
series and that observed for the Philadelphia series. The intermediate determination, at a body weight of 175 grams, was also
taken midway between the observed Philadelphia record and the
corresponding record for the London series — which is here low.
1.3
80
CRANIAL CAPACITY OF
ALBINO RATS
c.c.
^
PHILADELPHIA
© ^^^--^
RECORDS
^^'^""^^
j^-^
^..^-■^
® ^.^^
y^ ^
® ./ CHART 4.
■
BODY WEIGHT gms. |
100 120 140 160 180 200 220 240 260 280 300
Chart 4, showing the cranial capacity in cubic centimeters for the four albino
series. The values for the Philadelphia series are represented by a curve computed from formula (2). The values for the European series are entered separately. O = Paris series, D = London series, V = Vienna series.
Using these three points, Dr Hatai has kindly devised the following formula:
y = 1.02 log X - 0.00027 x - 0.596 (2)
where x is the body weight and y the cranial capacity.
The curve thus obtained is the one entered in chart 4 and used
as the standard from which to compute the deviations of the
records for the European series. . The European albino records
follow in about the same order as the records for the Norways,
i.e., the Paris series give the highest mean value, being above the
standard, while the London and Vienna series are slightly below
it.
These relations suggest that the conditions in the three European stations which act to modify ultimately the cranial capaci
90 HENRY H. DONALDSON
ty of the dried crania also act in a like manner on both the wild
Norways and the domesticated Albinos. Calculation shows that
the combined records for the European Albinos run somewhat
above those for the Philadelphia Albinos. The figures are given
in table 18.
These results suggest for consideration several important questions. As is seen in table 17, the mean cranial capacity of the
Paris Norway series is 0.4 per cent less than that of the Philadelphia series, while from table 16, we see that the Paris brain
weight is about 2.5 per cent greater. It would appear from this
that the Paris crania had shrunk about 3 per cent more than the
Philadelphia crania. Again table 17 shows the capacity of the
TABLE 18
Mus norvegicus alhinus. Showing the viean -percentage deviation in cranial capacity
of each of the three European albino series from the Philadelphia series taken as a
standard
MEAN PERCENTAGE
DEVIATION
Paris +4.9
London —0 . 1
Vienna —0 • 1
Average ! +1 -Q
London crania to be about 2.5 per cent less than that of the Philadelphia crania while the brain weights are nearly identical;
once more a greater relative shrinkage in the London series. The
same thing has probably happened in the case of the Vienna
series, but for this series the brain weight determinations are
lacking.
The albino records must also represent crania which have suffered more or less shrinkage characteristic for the series to which
they belong, but as table 18 shows, two of the series run close to
the Philadelphia standard, though slightly below it, while one,
the Paris series, is clearly above it. As the preparatory treatment
of all the skulls was the same, these variations in the amount of
shrinkage nmst find their explanations in vai'iations in the composition of the skull })ones — as represented by the amount of
BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 91
water, organic matter and salts in them and by their thickness.
Watson ('06) has shown that the constitution of the osseous system of the rat can be significantly modified by diet.
In the meantime it is clear that we cannot infer that the brain
weights in the several Norway series are related precisely as are
the cranial capacities.
2.4
2.3
2.2
2
2.0
1.9
CRANIAL CAPACITY
c.c.
CHART 5
NORWAY
PHILADELPHIA RECORDS •
EUROPEAN RECORDS
ALBINO.
PHILADELPHIA RECORDS
EUROPEAN RECORDS
BODY WEIGHT gms.
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1,7
1.6
1.5
1.4
80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380
Chart 5, cranial capacity based on European series only. Showing the cranial
capacity in cubic centimeters of the European series of Norways all combined,
contrasted with the computed value (formula 1) for the Philadelphia records and
similarly of the European series of Albinos all combined, contrasted with the computed value (formula 2) for the Philadelphia records. • = European series —
Norway. X = European series — Albinos.
However, bearing in mind that the cranial capacities of the
three European Norway series combined are probably as much as
2.1 per cent too low, and that so far as the tables 13 and 18 and
chart 4 show, the capacities of the combined European albino
series are slightly (1.6 per cent) above those for the Philadelphia
Albinos, it is possible to make a general comparison between the
two forms as found in Europe, in respect to their cranial capacity.
The data for this comparison are found in tables 12 and 13
and the averages for the European series there given are plotted
92
HENRY H. DONALDSON
in chart 5. In making these averages, the mean values for each
series are taken as they stand in the tables and are not weighted
for the number of cases to which each applies.
When the records for the European albino cranial capacity are
thus compared with those for the European norway, it is evident
that there are considerable differences between the two. The
approximate values of these differences can be determined in the
following way:
If we take as the standard the body weight values of the European albinos as given in each body weight group in table 13 and
TABLE 19
Showing the percentage values of the differences in cranial capacity between the European Albinos and the European Norways of like body weights. See chart 5. The
values in the fourth column have been read from chart 5
MEAN BODY
MEAN CRANIAL CAPAaiY
PERCENTAGE DIFFER
WEIGHT GROUP WEIGHT
Albinos
Norways
THE NORWAYS
grams
51-100 ' 90.0
101-150 :! 130.4
151-200 1 172.4
201-250 217.1
251-300 283.0
1.443*
1.517
1.652
1.761
1.860
1.570
1.725
1.860
1.960
2.070
(8.8)
13.7
12.6
11.1
11.3
Average . .
12.2
- There is in this weight group only the Paris record, see table 13 and chart 4.
The Paris record, which runs high, raises this value and hence diminishes the percentage difference given in the last column, thus slightly diminishing the general
average. Hence the record for the 51-100 grams body weight group is omitted in
making the final average.
enter also for these the cranial capacity as observed, and then
read from chart 5 the corresponding observed values for the cranial capacity of the European Norways, and enter these readings
also in table 19, we have before us the numbers which make it
poss-ible to compute the percentage differences between the albino
and the Norway records (see table 19).
Table 19 shows the average difference between the combined
European Albino and the combined European Norway records
to be 12.2 per cent.
BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 93
From the foregoing data on cranial capacity, we therefore conclude that there is no evidence that any of the European Norway
series represent a small brained strain which might have been the
source of the Albino variety.
The studies on the cranial capacity lead then to the same conclusion as was reached from the direct determinations of the
weight of the central nervous system and thus the particular
suggestion which we proposed to test is shown to be without
support. There remain however some minor aspects of these
results on cranial capacity which require further consideration.
TABLE 20
Showing the percentage values of the differences in brain weight between the Philadelphia Albinos and the Philadelphia Norioays of like body weight — using the
body loeights for the European Albinos as given in table 19. Data in column 3
are calculated from the formula for the albino brain tveight based on body weight
{Donaldson '08). Data in column 4 are calculated from the formula for the Norway
brain weight based on body weight {Donaldson and Hatai, '11)
MEAN BODY
WEIGHT
MEAN BRAIN WEIGHT
PERCENTAGE DIFFER
Albinos
Norways
THE NORWAYS
51-100
90.0
130.4
172.4
217.1
1.640
1.740
1.827
1.965
(11.4)*
101-150
12.9
151-200
1.814 2.068
1.873 2.152
14.0
201-250
14.9
251-300
283.0 1.941 2.249
15.8
Average .
14.4
- This entry omitted in making the final average so that this average may be
directly compared with the final average in table 19.
Before it was recognized that the amount of shrinkage of the
skulls in the different series was dissimilar, I had expected to find
the percentage differences between the cranial capacities of the
European Norways and European Albinos approximately equal
to the percentage differences between the brain weights of the
Philadelphia Norways and Philadelphia Albinos.
The data on brain weight which should be used for such a comparison are given in table 20.
94 HENRY H. DONALDSON
This table was formed by using the same body weights as are
given in table 19, but in place of the records for cranial capacity,
entering those for brain weight. The average percentage difference in the brain weight is seen to be 14.4 per cent or 2.2 points
higher than the corresponding value for the cranial capacity —
which is 12.2 per cent.
We have already found that according to the data in table 17,
the crania of the European Norways have shrunk 2.1 per cent more
than those of the Philadelphia Norways, and those of the European Albinos 1.6 per cent less than those of the Philadelphia
Albinos. Therefore if the average observed difference in the
cranial capacity (12.2 per cent) were corrected for the excessive
shrinkage of the European Norway crania, and the deficient
shrinkage of the European Albino crania (i.e., 2.1 + 1.6 = + 3.7
per cent) it would give a value of (12.2 + 3.7) 15.9 per cent as
that for the anticipated average difference in brain weight.
From table 20 the observed difference is seen to be 14.4 per
cent. It is to be remembered however that this last is based on
the brain weights of the Philadelphia forms and that we have
already found, table 16, the brain weight of the European Norways (Paris and London series) to be 1.2 per cent greater than
that of the Philadelphia Norways. If we use this as a correction,
then the average difference in brain weights becomes (14.4 -f- 1.2
per cent) 15.6 per cent, or very close to the difference found (15.9
per cent) when the cranial capacities are corrected for the varying
amounts of shrinkage shown by the several series.
Neither the nature of the data nor the method of comparison
will justify us in pushing this argument in detail, but the general
relations thus determined, clearly support the view that the difference in cranial capacity here found — when corrected for the
unequal shrinkage of the crania in the two forms of the European
rats, and for the slight excess in the brain weight of the European
Norways, approximates the difference in brain weights which we
should expect to find between the two European forms if the
European and American rats were nearly alike in the relative
weight of their central nervous systems.
BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 95
There is still to be noted another dissimilarity between the
percentage differences of the cranial capacities (table 19) as compared with the corresponding differences in brain weight (table 20).
This dissimilarity also is due to the manner in which the cranium
shrinks — in this instance according to age. It will be seen by
looking at table 20 that the percentage difference in the brain
weight increases regularly with increasing body weight. On the
other hand, the corresponding records for cranial capacity in table
19 indicate a decrease with increasing body weight. Here again
we should have expected the cranial capacity records to behave
in the same way as the brain weight records, but they do not. We
find the explanation for this disagreement in the shrinkage of the
crania as influenced by age. The argument is as follows:
As is well known, in any series of crania those from the younger
animals contain a larger proportion of water as well as more
organic matter and have thinner bones and hence shrink relatively more when dried than do the crania from the older animals. We assume then that in any series of crania, loss of water
and thickening of the bones increases with advancing age, and
concomitantly, shrinkage on drying decreases with advancing age.
In the heaviest body weight group of the albinos (table 19)
the crania are the more mature and so shrink less than the crania
of the Norways of like body weight — which are somewhat less
mature. This statement is based on the fact that the Norway
rat, although it has probably the same span of life as the Albino
(Donaldson and Hatai, '11) has nevertheless a much greater range
in body weight and hence in general for a given body weight it
must be younger than the corresponding Albinos, although the
difference in the relative shrinkage for the heaviest body weight
groups may be absolutely small. It follows from what has been
said about the range of body weight in relation to the span of life
in the Norways that an equal diminution in mean body weight,
say 50 grams, implies a greater diminution in age for the Albino
than for the Norway. According to the foregoing reasoning, this
should be followed by a relatively increasing shrinkage in the
albino crania, and this is the interpretation of the values given in
the last column of table 19.
96 HENRY H. DONALDSON
To bring together the observations and comments on cranial
capacity which have just been presented, it appears that while
the European Norways are shown to be distinct from the European
Albinos as regards their cranial capacity, yet the interpretation of
the direct observations is necessarily so modified by the shrinkage
of the crania that in the case of any particular series, we can infer
only in a general way from the cranial capacity to the brain weight.
CONCLUSIONS
1. In the case of the wild Norway rat, which entered western
Europe about the beginning of the eighteenth century, and the
eastern United States about 1775, the observations on the constitution of the populations, the general body form, the weight of
the central nervous system and the cranial capacity, show that
it is at the present time essentially similar in these respects in the
two continents.
2. The observations on the albino rat from different stations
indicate that this variety is also essentially similar in the two
continents. Therefore there is no evidence to support the view
that the Albino was derived from a strain of the Norway having a relatively small central nervous system.
3. Logically this result does not preclude the possibility of such
an origin, but it does indicate on the other hand the absence of
present evidence in favor of it.
4. That the Norway rats from the three stations in Europe are
very similar to the Philadelphia Norways, despite the difference
in station and the wandering of those that have crossed the sea,
is probably due to the fact that the series of rats which have here
been compared represent those which kept close to man, and all
of which lived among food conditions and other surroundings
characteristic of large cities; conditions and surroundings which
are much the same in western Europe and eastern America.
A like explanation applies also to the similarity found among the
Albinos from these two regions, and perhaps even more forcibly,
as the treatment of these caged animals pi'obably represents a
still more uniform environment than that which the Norways
experience in their wild life.
BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 97
At some future time it will be of interest to examine the Norways of still other countries — those from India for example — ■
where we should expect the food conditions to be quite different
from those obtaining in western Europe and North America.
5. The capacity of the dried cranium of the rat is modified
by age and by the amount of calcification to such an extent
that the data for capacity cannot be transformed into those for
brain weight without making correction for several fluctuating
conditions.
6. The constancy of the foregoing characters in the rats (both
Norway and Albino) from western Europe and easter America
indicates that for the purpose of further general studies, the two
populations may be considered as essentially similar.
LITERATURE CITED
Chisolm, R. a. 1911 On the size and growth of the blood in tame rats. Quart.
J. of Exper. Physiol., vol. 4, no. 3, pp. 207-229.
Cunningham, D. J. 1909 Text book of anatomy. 3d edition. William Wood
and Co., New York.
Donaldson, H. H. 1909 On the relation of the body length to the body weight
and to the weight of the brain and of the spinal cord in the albino rat
(Mus norvegicus var. albus). Jour. Comp. Neur., vol. 19, no. 2, pp.
155-167.
Donaldson, H. H. and Hatai, S. 1911 A comparison of the Norway rat with the
albino rat in respect to body length, brain weight, spinal cord weight
and the percentage of water in both the brain and the spinal cord.
Jour. Comp. Neur., vol. 21, no. 5, pp. 417-^58.
Donaldson, H. H. 1912 On the weight of the crania of Norway and albino
rats from three stations in western Europe and one station in the
United States. Anat. Record, vol. 5, no. 2.
Hatai, S. 1907 Studies on the variation and correlation of skull measurements
in both sexes of mature albino rats (Mus norvegicus var. albus). Am.
Jour. Anat., vol. 7, no. 4, pp. 423^41.
Lantz, David E. 1909 The brown rat in the United States. U. S. Department
of Agriculture, Biological Survey, Bull. no. 33, pp. 9-54.
Watson, Chalmers 1906 The influencp of an excessive meat diet on the osseous system. Proc. Roy. Soc. Edin.^ 1906-7, vol. 27, part 1, (no. 1).
EXPERIMENTAL STUDIES OF PARALYSES IN DOGS
AFTER MECHANICAL LESIONS IN THEIR SPINAL
CORDS WITH A NOTE ON 'FUSION' ATTEMPTED
IN THE CAUDA EQUINAS OR THE SCIATIC NERVES
HENRY O. FEISS
From the H. K. Cushing Laboratory of Experimental Medicine, Western Reserve
University
TWENTY-SEVEN FIGURES
CONTENTS
Introduction : 100
Reasons for the research 100
The production of the lesion 101
Method of studying the surviving animals 101
Study of autopsy material 102
Part 1. Clinical improvement after the production of the lesion in relation
to the histological findings at different stages 102
Character of the clinical improvement 103
Histological summary 103
Inferences from the above 104
Bearings of above inferences on infantile paralysis 105
Part 2. The localization of centers in the lumbo-sacral cord 106
Method of study and reasoning 106
Inferences from the individual experiments : summary 107
Correlation of data derived from individual experiments 109
A. Control of joints, et cetera 109
B. Knee jerks 109
C. Sensation 109
D. Anal reflex 109
E. Control of sphincters 109
F. Conclusion HO
Comparison of inferences with current views on the subject 110
Significance of cell-groups in grey matter of the spinal cord 113
Part 3. Nerve fusion attempted in the caudas and the sciatic nerves in animals paralyzed by mechanical lesions in the cord 113
The aim of the procedure 113
Experimental data 114
Discussion 117
99
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 2
APRIL, 1912
100 HENRY O. FEISS
INTRODUCTION
Reasons for the research
The present series of experiments was begun in the spring of
1908 with the production of mechanical lesions in the lumbar
spinal cords of dogs. The object was to bring about distinct
motor paralyses. After the animals had reached permanent
stages in the paralysis, so that there was no question about degeneration in the roots and peripheral nerves, it was planned to
attempt to distort the nerve-patterns in these structures, using for
this purpose a method heretofore apparently untried. This
method is referred to as nerve 'fusion,' and consists simply in
uniting two or more nerves by tying them together with absorbable ligatures.
In carrying out the plan given, it early became apparent that
the subject of nerve 'fusion' was a research in itself, requiring
many special experiments. Fusions were therefore attempted
on normal nerves where no central lesions had been produced.
A preliminary report of this work has already appeared^ and
we have been able to offer some evidence that after nerves are
united by this method, a certain amount of distortion of pattern may take place.
However, even if changes in nerve-pattern are obtainable by
the union of nerves which are normal, it does not follow that the
same changes may be expected where there has been a central
lesion. Fatty degeneration takes place in the paralyzed muscles
and in the nerve trunks themselves, the degenerated tracts close
up and become replaced by new connective tissue.
Therefore, the original design of producing central lesions and
later trying nerve fusions has been carried out. In the course
of this research two other issues have developed which proved to
be of equal if not greater interest. It was shown that after a
lesion was produced in the spinal cord by the method which will
be outlined, a very characteristic spontaneous recovery took
place similar to the early recovery often seen in infantile
' Fciss: Boston Medical nnd Surgical Journ., May 11, 1911.
PARALYSES IN DOGS 101
paralysis, and it was found that the material furnished data for
adding to the precision of our knowledge on the localization in
the lumbo-sacral cord certain nuclei of the pelvic viscera and of
the muscles of the hind limb and tail.
This report may therefore, be divided into three parts; in the
first part attempting to account for the clinical improvement
occurring after the lesion, in the second part showing the relation of the autopsy findings to the peripheral and visceral palsies
produced, and in the third part discussing the subject of fusion
and giving a brief account of some experiments in which, some
months after the lesion, this procedure was attempted.
The production of the lesion
The lesions were made subdurally through a single trephine
opening, usually at the 4th or 5th lumbar spine. The instrument for the purpose (fig. 1) was L-shaped, the longer arm forming the handle and the shorter shaped into a thin blade. This
was entered through the dura in the median line and then moved
laterally with sufficient force to crush the cord substance. Both
unilateral and bilateral lesions were attempted. The operations
were done under complete ether anesthesia with the usual precautions for asepsis. All told, lesions were attempted in some seventyfive animals, but of course, on account of various causes, including
an epidemic of distemper, the majority of animals were lost.
Method of studying the surviving animals
Observations were made from day to day and notes were made
on the changes. At intervals of 2 or 3 months, each dog was
studied more systematically, according to the following routine:
1. Attitude
2. Gait. Nature of limp if present
3. Active movements : rump, hips, knees, ankles, paws and tail
4. Passive movements: rump, hips, knees, ankles and paws
5. Response to stimulation; sharp point applied to skin of various parts of limb
6. Response of paw to heat with immersion in hot water (heat-pain sense)
7. Temperature of skin between toes
102 HENRY O. FEISS
8. Measurements. Circumferences above paw, ankle and knee
9. Reflexes: knee jerks; anal reflex (observed by inserting glass rod into anus)
10. Control of sphincters (based on ordinary clinical observations)
11. Response to faradism; applied to various parts of limb
12. Remarks
13. Photograph
In a few of the dogs data bearing on spinal localization could
be obtained by direct stimulation of peripheral nerves, which
was done at the time of the secondary operations of nerve fusion.
Study of autopsy material
The spinal cords were studied in twenty of the cases. In six
of them proper identification of the roots could not be made,
owing to scar. The other fourteen were each mounted on cardboard, and the roots spread out, stitched down, and properly
numbered. The count was made from the thirteenth, using the
last rib as a land-mark. Each mounted specimen was sketched
and placed in Miiller's fluid.
The boundaries of the cord segments were usually estimated
by means of their relations to dural root exits, this relationship
having been based on a number of dissections of normal cords.
After proper hardening, the cord was cut transversely into a
number of pieces without attempting to remove the dura, so as
not to disturb the rootlets within. The exact location of each
of these cuts in relation to dural root exits was indicated on the
sketch. The pieces were cut 2 to 3 mm. thick and imbedded in
celloidin. Sections from each piece were stained by at least three
methods, Hematoxylin-eosin, Van Gieson and Weigert-Pal.
PART 1. CLINICAL IMPROVEMENT AFTER THE PRODUCTION OF
THE LESION IN RELATION TO THE HISTOLOGICAL
FINDINGS AT DIFFERENT STAGES
This portion of the research is based on the studies of twenty
dogs and their spinal cords. The important points are summarized in table 1. Glancing at this, it is seen that after such a
lesion as described, almost all the animals showed more or less
clinical improvement. It is further seen that this improvement
Number of days
laboratory after lesion that
When first noticed
No improvement
Distinct improvement
noted on 5th day
Distinct improvement
noted on 5th day
Distinct improvement
noted on 6th day
Distinct improvement
noted on 11th day
Distinct improvement
noted on 9th day
No improvement
Distinct improvement
noted on 9th day ,
Gradual improvement '
Gradual improvement
One month after leelo
Improvement
Improvement
Improvement
Improvement
No change
No change
Improvement
Improvement
Gradual improvement | Improvement
Distinct improvement i
Distinct improvement j
noted on I3th day !
Gradual improvement I
Gradual improvement
Gradual improvement
Distinct improvement
noted on 6th day
Distinct improvement
noted on 6th day
Gradual improvement
Gradual improvement
Improvement
Improvement
Improvement
Improvement
Improvement
Improvement
Improvement
Improvement
Improvement
Two moothfl after
No change
No change
- No change
j Improvement
Improvement
1 Slight improvement
Improvement
I Improvement
Improvement
Slight improvement
j Slight improvej ment
I Slight improvement
Improvement
Slight improvement
Three moDthe o
I Slight improvement
Slight improve- 1
I ment I
No change
I No change
I No change
No change
i Slight improveI ment
No change
No change
- Slight improvement
I Slight improveI ment
Mass of debris including broken down myelin and blood, which is entered by granulation tissue from pia and dura. This
granulation tissue more dense toward periphery. In the interior there are young fibro blasts with elongated nuclei.
Also many new capillaries. Compound granular cells, small round cells and leucocytes also present. Areas of beginning
necrosis in neighboring grey matter.
Similar to above.
Marked formation of cavity divided into compartments. Granulation tissue denser than above. Many myelin droplets
left. Some fibroblasts and compound granular cells. Less d6bris than in above. Leucocytes and round cells in new
connect, tissue. Little repair in grey matter. Some ant. horn cells swollen and pale.
Similar to above.
Similar to above.
Similar to above.
Dense scar with small cavities adjoining. These contain a little debris and a few myelin drops small in size. Some small
nerve fibers, perhaps new, entering cavities. Many round cells.
Zone of dense scar from dura. Next a zone of less well organized connect, tissue containing in its meshes compound granular cells and myelin drops. Next a zone of a relatively few fibro blasts and myelin drops, debris in large amounts and
old blood. Finally normal cord substance. Some ant. horn cells are bloated.
One main large cavity, which is lined by thin layer of new connect, tissue. Ant. horn cells show bloating and chromatolysia.
Dense scar with large patches of round cells. Many leucocytes and new vessels.
Much dense scar. Two large cavities still containing the remains of myelin in small amounts.
Distortion of grey matter.
Ant. horn cells often bloated and show chromatolysis.
Much dense scar. Large cavity, which tends to follow outline of grey matter.
Distortion of grey matter. Vacuolation of ant. horn cells.
Much dense scar containing cavities.
Ant. horn cells pale and bloated, having lost their polygonal shapes.
Dense scar and cavities. Broken down tissue in grey matter.
Vacuolation of ant. horn cells.
Dense scar containing cavities.
Dense scar, debris and light connective tissue. Cavities.
Distortion of grey matter.
Light connect, tissue and areas of partial necrosis in grey matter. Some dense scar with cavities.
] 2 large cavities, one of which follows outlines of grey matter. Dense scar.
1 large cavity. Thick e
• in du
Dense and light scar, one cavity, d6bris and remains of myelii
Areas of necrosis in grey matter.
Ant. horn cells often swollen, bloated and pale.
Marked degeneration
in some of the fibers
Similar to above
Similar to above
Similar to above
Complete or almost
complete degen. of
some of the fibers
Similar to above
Similar to above
Some remains of broken down m3'elin in
fibers
Some beginning regeneration
Some fibers show signs
of degeneration.
Others suggest new
regeneration
Similar to above
Increase in connect, tissue in nerve trunks
Similar to above
Similar to above
Signs of new regeneration in roots
Good regeneration of
many fibers
Similar to above
Similar to above
Similar to above
Similar to above
PARALYSES IN DOGS 103
fell into two stages, (1) a sudden improvement occurring in the
first or second week, and (2) a slow improvement continuing for
three or four months.
Character of the clinical irnprovement
The paralysis immediately following the operation was often
a complete paraplegia, sometimes of one leg only, and rarely of the
tail and sphincters. The dog lay in the kennel, seemingly stunned
and not caring for food. He appeared feverish and thirsty.
After a day or two, in spite of the paralysis, he made some attempt
to get over the ground, with but partial success. The sudden
improvement in the first or second week was often very marked,
a paraplegia sometimes changing into a mere turning of one paw.
Figs. 2, 3, 4 and 5 show characteristic changes in two of the dogs.
Whether or not the improvement began suddenly, there was
always a period of gradual recovery ending in a permanent state
of residual paralysis.
The question is, how much of the improvement is based on
changes which are histologically demonstrable? The table (table
1) indicates what the chief histological changes were (the topography of ten of the lesions is studied in Part 2).
Histological summary
In the early autopsies the location of the lesion was evidenced
by a mass of debris, including broken down myelin in drops,
leucocytes and round cells in clumps. A mass of granulation
tissue had formed along the dura, at the place of injury. This
entered the mass of debris. In this stage, cavities were not
apparent, but in the neighboring grey matter were small areas
of beginning necrosis.
In animals autopsied at the end of one month, the most noteworthy thing was the appearance of cavity-like spaces. These
were formed of connective tissue bands some of which had become
well defined owing to the partial removal of the tissue debris.
By this time the scar connected with the dura had become 'quite
dense.
104 HENRY O. FEISS
At the end of two to three months, the sections showed the permanent histological characteristics of the lesion. These were
either cavity spaces or scar, or both. The cavity spaces were
sometimes sharply circumscribed, and occasionally their outlines
corresponded to the original outlines of the grey matter. In general, it seemed that the amount of scar depended on the amount
of direct injury to the pia and dura, and the size of the cavityspaces on the extent of the original destruction of cord substance,
although of course, the extent of the original cavities could not
be completely judged on account of tissue repair. In some places
the grey matter showed marked distortion of outline, suggesting
contraction.
As to signs of nerve regeneration in the cord, one occasionally
saw among the debris and granulation tissue small fibers with
faint coats of myelin. But of course, there was no way of telling
whether these indicated repair; if they did it could have been
slight only.
In all stages, one saw striking changes in the ganglion cells of
the gray matter, near the lesion. These consisted in alterations
in size, shape and staining, reactions as well as chromatolysis and
vacuolation.
Inferences from the above
Judging from the histological condition one could divide the
anatomical appearances into two stages, roughly corresponding
to the two stages in the clinical improvement. It seemed likely
that the early improvement was partially due to the removal of
tissue debris, because the cavities became apparent about that
time. Also as shown clinically, by the swelling about the wound,
there was at first marked fluid exudate, the absorption or escape
of which was undoubtedly a factor in that improvement.
As to the more gradual improvement that supervened in most
of the cases, disregarding the anatomic evidence of repair of nerve
tissue in the cord itself, as being too slight to explain the marked
restoration of function, there are four other explanations to be
considered: (1), actual regeneration of nerve fibers in roots and
peripheral nerves; (2), vicarious activity of nerves and muscles
PARALYSES IN DOGS 105
(including employment oi other paths in the cord); (3), failure
of many of the neurones originally pressed on by the exudate to
degenerate completely, so that with removal of the exudate they
recovered their functions; (4), changes in subjective state in the
animal as brought about by lessened discomfort. (The last two
explanations might also apply to the early improvement.) We
cannot say which of these factors were most important — in fact,
it is possible that all of them had a share in explaining the clinical change for the better.
Previous researches on the subject
That marked restoration of power may occur after lesions in
the central nervous system is well known. This applies both
to cortical extirpations, ^ and co hemisections in the cord. The
fact that there is also considerable restoration of power after
complete section would seem to indicate that there might be
regeneration across the scar. This has been actually observed
in some of the lower animals."* Brown-Sequard noted it in fishes
and Fraisse in amphibians. But in higher animals it has not been
observed,^ and for this reason, in cases of hemisection restoration
of the clinical state has been said to be partially due to the employment of paths on the contralateral side. Be that as it may,
it is not necessary to base the restoration of function on nerve
repair across the scar because the clinical improvement seemed
practically as great in our cases where, on account of the extent
of the lesion, conditions for nerve repair were not favorable and
where, moreover, signs of such repair were scarcely to be made out.
Bearing of above inferences on infantile -paralysis
The spontaneous restoration of power noted in our dogs is
very similar to that often observed in infantile paralysis. This
applies both to the early and late improvement. The former,
' Sherrington: Integrative action of the nervous system, 1906, p. 277.
3 Weiss: Sitz. d. Akad. d. k., Wissensch., Wien, 1879, Bd. 80.
- Bechterew: Functionen der Nerven Centra, 1908, vol. 1, p. 652.
- Schiefferdecker : Virchow's Archiv, Bd. 67.
106 HENRY O, FEISS
also in that disease, is at least partially due to the removal of
inflammatory material, somewhat as in the conditions described
above, where the exudate is dependent only on simple mechanical lesions, although part of the recovery in infantile paralysis
may be related to cell changes which take place as a result of
the expulsion or neutralization of specific toxines. As regards
the later improvement in that disease, one is just as much in
doubt as to which of the factors above mentioned is of greatest
significance. '
It is plain, however, that the spontaneous recovery observed
in infantile paralysis is perhaps an attribute less characteristic
of the disease than of the anatomical structures which the disease attacks. Whether it is a clean section, or a crushing lesion
or an inflammation set up by some virus, there are certain succeeding manifestations that seem to be common to all these antecedents, and these manifestations are exhibited with striking
clearness simply because of the fact that in the central nervous
system, a relatively small anatomical change affects an extremely
large physiological sphere.
PART 2. THE LOCALIZATION OF CENTERS IN THE LUMBOSACRAL CORD
Method of study and reasoning
This part of the research is baspd on ten of the experiments.
The study of data furnished by this material is summarized in
tabular form (table 2) and each experiment is illustrated with a
photograph, and a diagram based on the sketch made at the
autopsy. In these diagrams only direct involvements due to
the lesions are indicated. The degenerations were partly due
to secondary operations, and are therefore best omitted, because
under the circumstances tney throw no light on the localization.
In handling the data, each case is analyzed for itself and the
inferences individually derived are collated according to the important clinical and physiological headings under which each was
studied. The cord segments were numbered according to the
roots, calling the root issuing beneath the last ril), the 13th.
■■••FOiira or
BBrLazBS
BPHINCTEB9
ExpianuBNT
cowrnOL or JOIMTB
LBO TO FOIMT
PAW TO HBAT
(PAW)
(See dla^ms)
POBtnVB conclduoks roB individital
Knee Jeik
Anal
Anna
Bhddiir
64
Paralysis of dorsal flex, of left paw
Poor on
No test
Absent on
Sluggish
N
N
In upper 7th L. seg. post, horns and cols, on both sides.
Dorsal flexion of paw and ankle (E. P.), in dorsal part of
and ankle
both legs
left
On left, lat. col. and upper | of ant. horn. In 1st S. seg. j ant. horn of upper 7th L.
Direct stimulation evoked no re
cent, part of grey matter on left. In 5th, 6th, 7th and 1st j
sponse in left E. P.
S. seg. postero-mesial col. 5th and 6th post, roots.
78
Paralysis of dorsal flexion of right
Poor on
Poor on
Absent on
Sluggish
N
N
In naid. 4th L. seg., lower part of rt. ant. horn and adjoining Dorsal flexion of paw and ankle (E. P.) — in lower 6th L.
paw and ankle. Weak extension
rt. leg
right
right
col. In high 5th L. seg., entire rt. ant. horn and adjoining i I. P. control lower (in 7th)
of rt. hip and knee
col. In low. 5th L. seg., entire rt. half of cord except ant. Extens. of hip and knee in 5th
Direct stimulation evoked no re
mesial col. In mid. 6th L. seg., whole cord except ant. Gap between centers of lower and upper leg, perhaps con
sponse in right E. P.
cols, and lower part of It. lat. In upper 7th rt. ventromesial col. very narrow 4th, 5th and 6th rt. ant. roots.
taining centers of hamstrings
86
Paralysis of rt. paw and ankle and
Poor on
Poor on
Absent on
Sluggish
N
Weak
In upper 5th L. seg., rt. side of cord except pyram. tract, also
Dorsal flex, of paw and ankle (E. P.) in mid. 6th
of dorsal flex, of left paw and
rt. leg
right
right
It. ant. horn. In low. 5th L. seg. rt. side of cord. Inmid.
Plantar flex, of paw and ankle (I. P. ) in inner dorsal part of
ankle. Weak extension of rt.
Weak on
6th whole cord except It. ant. col. and small part of It.
ant. horn of upper 7th
hip and knee and some weakness
left
ant. horn. In upper 7th inner } of rt. ant. horn.
Extens. of hip and knee in 5th
of It. hip and knee
5th and part of 6th rt. and It. ant. and post, roots and 4th
Direct stimulation evoked no re
rt. ant. root.
sponse in either E. P. and very
slight (of toes only) in rt. 1. P.
60
Slight weakness in dorsal flex, of
rt. paw and ankle
N
N
N
Sluggish
N
N
In mid. 6th all of grey matter and dorsal and ventral cols,
which are partly spared on left. In upper 7th rt. ant.
horn, rt. lat. col., both ant. cols, and lower f of It. ant.
horn. 6th rt. post, and 6th and 7th rt. ant. roots.
Dorsal flex, of paw and ankle (E. P. ) partly in upper 7th.
Gap between centers of lower and upper leg
65
Paralysis of entire left leg except
Poor on
No test
Absent on
Sluggish
N
N
In upper 6th whole left of cord, and dorso- and ventro-mesial
Control of most of leg in 5th seg. and those below
for flex, of hip. Weak extension
left
left
cols, and inner part of grey matter on rt. In low. 6th It.
Point sensation passes through 5th post, root
of knee and weak flex, of hip on
Weak on
ant. horn and It. antero-lat. col. ; also inner part of rt. ant.
right
right
horn. In low. 7th outer part of It. ant. horn and It. anterolat. col. In 2d Sac. grey matter about central canal. 5th
6tb, 7th and 1st It. ant. roots; 5th and 6th It. post, roots;
6th rt. ant. root.
75
Weakness of gluteals and hamstrings
Poor on
Poor on
Absent on
N
N
N
In mid. 6th dorsal cols, and inner part of base of rt. post.
Sciatic centers in 7th L. and lat Sac.
on rt. hip flexed and knee straight
right
right
right
horn. In upper 7th rt. side of cord and dorsal col. and
and stiff
inner part of grey matter on It. In 1st Sac. rt. side of cord
Paw paralyzed and flaccid
and inner part of It. ant. horn. 6th and 7th rt. post, horns.
70
Spastic loss of control of hind parts
from pelvis down. Weakness of
erector spinae. glutei and quadriceps. Hamstrings fairly good
Poor on
left
N
N
N
N
N
In mid. 4th rt. ant. horn. In upper 5th It. post, and all of
antero-mesial cols. rt. ant. horn, most of It. grey matter. In
mid. 5th all of cord except rt. post. horn. In low. 5th whole
cord. In high 6th It. of cord. In mid. 6th ant. cols, and lower
Some crural and gluteal centers in upper 5th. Homatringa
below mid. 6th
Transection in lower 5th cuts ofif brain control of lower leg
Point sensation passes through 4th post, root
part of ant. horns. 4th, 5th, and part of 6th rt. and It. \ Heat-pain sensation above mid. 5th
ant. roots 4th It. post. root.
K.J. anal reflex, control of sphincters below upper 6th
72
Flaccid paralysis of hind parts from
Poor on
No test
Absent on
No test
Weak
Weak
In mid. 5th, base of dorsal cols, part of rt. ant. root. In
Control of hind parts including sensation, K. J. 's and sphinc
pelvis down.
both
both
low. 5th, all of grey matter and dorsal and vent. cols, except left post, horn and small part of vent. col. adjoining.
In mid. 6th all of grey matter and rt. ventral and lat. cols.
In mid. 7th rt. ant. horn and inner part of It. grey matter.
5th, 6th and part of 7th rt. It. ant. roots, rt. 5th post. root.
ters in 5th to 7th inclusive
68
Paralysis of tail and slight weakness
Poor on
Poor on
N
Sluggish
Weak
Weak
In mid. 6th dorso-mesial col. In mid. 7th rt. side of cord.
Control of motion and sensation to point and heat-pain in
in dorsal flex, of rt. paw.
tail
On legs
N
tail
dorso- and ventro-mesial cols, and inner part of It. grey
matter. In low 1st Sac, whole of cord (conus). 5tfa and
6th rt. ant. and post, roots.
tail in 7th L. and 1st S.
Anal reflex and control of sphincters in 7th L. and Ist Sac.
73
Paralysis of tail
Poor on
tail
Poor on
tail
N
Sluggish
N
Weak
In upper 7th, all of grey matter except It. post, horn; also
vent. cols, and lower part of rt. lat. col. and rt. dorsal
col. In lower 7th entire cord (conus).
Control of motion and senaation to point and heat-pain in
tail in 7th L.
Anal reflex and control of bladder in 7th L.
Lattor N - normal. E. P. • external popliteal. I. P. > mteroal popliteal
PARALYSES IN DOGS 107
Unfortunately, the ribs themselves were not counted, so that
the possibility of variation must not be lost sight of, as a source
of error.
The most pertinent information is that obtained in the individual case by comparing rights and lefts. Other things being equal,
one may in certain cases, ascribe a unilateral effect to a corresponding unilateral lesion. In the same way by proper elimination,
bilateral effects may sometimes be ascribed to bilateral lesions.
It will be apparent that the collation of all the evidence according
to numerical segments offers less exact conclusions than those
which can be derived in the same individual and more especially
with reference to the relative position of centers. But by comparing relationships and detecting correspondence, certain inferences of significance may be obtained. Aside from the assumption that the upper leg centers are, generally speaking, higher
than those of the lower leg, no further assumptions were used,
except, of course, such as are based on the classical conceptions
of the functions of anterior and posterior roots and of the white
and grey matter of the spinal cord.
Inferences from individual experiments: summary
Experifnent 64- (Figs. 6 and 7.) External popliteal paralysis on
left not accounted for by slight anterior root damage as there was similar damage on right where there was no paralysis. Therefore the external popliteal centers must be in the upper 7th lumbar segment, and by
comparing right and left anterior horns, they must be in the dorsal twothirds of the horn. Loss of left knee jerk accounted for by involvement of 5th and 6th posterior roots. If internal popliteal centers are
at the level of or below the external popliteal centers (see Experiments 78
and 86), paths for voluntary control seem to run in the anterior column.
Experiment 78. (Figs. 8 and 9.) Weakness of right knee and hip
best explained by involvement in 5th lumbar segment and anterior
root jBlaments attached. As lesion in grey matter of middle 6th lumbar
leg is bilateral and left leg seemed good, it could not account for paralysis of right external popliteal, which is consequently traceable to damage
of right anterior roots attached to lower 6th and upper 7th lumbar segments. Both internal popliteals being good, their centers must be lower
than external popliteal centers, for they could not be higher on account,
of bilateral lesion just above, which les.on also suggests a possible gap
between upper and lower leg centers. Extinction of right knee jerk
explained by 5th and 6th anterior root involvement. Voluntary dor
108 HENRY O. FEISS
sal and plantar flexion of left paw and ankle, and plantar flexion of right
seems possible with only anterior columns open.
Experiment 86. (Figs. 10 and 11.) External popliteal paralysis on
both sides due to damage in middle 6th and lumbar segments and roots
attached. Almost complete paralysis of internal popliteal on right
and not on left corresponds to lesion in upper 7th lumbar segment.
Loss of point and heat-pain sensation on right and not on left explained
by lesion in right half of cord in 5th lumbar segment. The difference
in damage to grey matter in lower 6th and upper 7th lumbar segments
must account for preservation of left knee jerk. As internal popliteal
is good on left and its centers are in upper 7th lumbar segment, impulses
from the brain to its synapses must have passed through the marginal
portion of the anterior column in the segment above.
Experiment 69. (Figs. 12 and 13.) The difference between the right
and left anterior horn involvement in the upper 7th might explain the
weakness of the right external popliteal. Lesion in 6th lumbar segment
suggests a gap between upper and lower leg centers. This lesion seems
to have had no effect on either knee jerk or on sensations, suggesting
that these latter must have entered through upper 6th rootlets or higher.
As the centers presiding over control of right paw may be presumed to
be below the 5th lumbar segment, the extent of the lesion might denote
that such control was cut off on that side. Therefore, as the dog used
the paw quite well (except for the external popliteal weakness mentioned)
it is possible that impulses crossed from the other side, where the lateral column was good.
Experirnent 65. (Figs. 14 and 15.) The extensive paralysis of the
left leg and paw together with loss of knee jerk, best accounted for by
severe root involvement, while the weakness in the right upper leg is
accounted for by damage to anterior horn in lower 6th lumbar segment
and some of the 6th anterior root filaments.
Experiment 75. (Figs. 16 and 17.) Here permanent flexure of right
hip and stiffness of knee, perhaps due to weakness of gluteals and hamstrings respectively, caused by damage of 5th, 6th and 7th anterior
roots. The lower leg paralysis explained by lesion in 7th lumbar and
1st sacral segments. Loss of right knee jerk explained by damage to
6th posterior root.
Experiment 70. (Figs. 18 and 19.) The lesion in lower part of 5th
lumbar segment involved entire cord, practically acting as a trans-section. This accounts for loss of control and spasticity of hind parts,
and places most of leg centers below that segment. It is likely that
preservation of knee jerk, anal reflex and control of sphincters is due to
sparing of centers below middle 6th lumbar segment (the anterior roots
being also destroyed above that level).
Experiment 72. (Figs. 20 and 21.) The lesion in upper 5th, 6th and
7th lumbar segments, with the corresponding anterior root damage accounts for loss of control of hind parts, including point sensation, knee
jerks and sphincters.
Experiment 68. (Figs. 22 and 23.) Impairment of control of motion,
point and heat-pain sensation of tail, together with impairment of anal
PARALYSES IN DOGS 109
reflex and sphincteric control, all accounted for by lesion in 7th lumbar
and 1st sacral segments. Slight paralysis of right paw also explained
by damage to right anterior roots.
' Experiment 73. (Figs. 24 and 25.) Impairment of control of motion,
point and heat-pain sensation in tail, together with impairment of anal
reflex and bladder control, all accounted for by lesion in the 7th lumbar
segment.
Correlation of data derived from individual experiments
A. Control of joints. Upper leg centers are mostly in the
5th and 6th lumbar segments, that is, about the level of the 4th
dural root exit. Lower leg centers are in the lower 6th and the
7th lumbar segments, that is, at the level of the 5th dural root
exits. Nuclei of the external popliteal, the internal popliteal
and the tail are somewhat circumscribed and relatively isolated,
and the nucleus of the external popliteal is, as a whole, higher
than that of the internal popliteal. There may be some overlapping of nuclei, but in one portion of the cord, namely, the middle 6th lumbar segment, there seem to be relatively few centers,
the nuclei of the upper and lower leg seeming to be respectively
above and below this apparent gap. (Possibly the hamstring
centers lie here.)
It is suggested that the anterior columns contain fibers from
the brain which convey volitional impulses.
B. Knee jerks. Its extinction or weakening is consistent with
corresponding damage to either the roots or grey matter of the
5th and 6th lumbar segments.
C. Sensation. As to point sensation of the whole leg, the 4th
and 5th posterior roots seem important links in the afferent chain.
As to heat-pain sensation of the paw (studied by immersion in
hot water), the test was omitted in three of the experiments and
was always accompanied by loss of point sensation. In one case
however (Experiment 70), point sensation was lost without
corresponding impairment of heat-pain sensation in paw.
D. Anal reflex. This test was omitted in one case, found
impaired in seven and normal in two.
E. Control of sphincters. Their centers lie below the 6th
lumbar segment. It is suggested by comparison of two cases
110 HENRY O. FEISS
(Experiments 68 and 73) that the bladder centers are higher than
the anal centers. Sphincteric centers are very close to tail centers (5th dural exit).
F. Conclusion. Inferences cannot be drawn for every point
investigated, but there is significance to certain isolated facts,
such for example, as pertains to the relative isolation of the external popliteal and internal popliteal centers, suggesting perhaps
that these nerves, which on account of their individual spheres
of distribution control the best coordinated joint movements, have
their nuclei relatively best defined. The main suggestion is that
the grouping of cells seems to correspond at least roughly to the
gathering of fibers in individual peripheral nerves.
Comparison of above inferences with current views on the subject
As regards the cases where preservatipn of voluntary control
in certain muscles seemed to depend on paths in the anterior
columns, which alone were open, other experiments are on record, which show that in dogs and other animals, these columns
do convey motor fibers from the brain. There is also the possibility of the employment of paths on the contralateral side (cf.
Part 1) and in one of our cases (Experiment 69) this seems to
be the only explanation for preservation of control of the paw, for
the lesion had blocked all the homolateral paths higher up.
With reference to the knee jerk our localization in the 5th and
6th lumbar segments corresponds to Sherrington's more accurate
findings.^
As to sensations, anal reflex and relative warmth of the paws,
our findings are too few to be entitled to colligation with those
of others.
The most important question that we have to consider is the
significance of the cell-groups in the grey matter of the cord.
Three methods have been previously used to investigate thit
point, the first being that of direct stimulation of spinal roots.
The findings depend on the presumption that the cells of origin
'Bechterew: ruiiotioTion der Ncrven Centra, 1908, vol. 2, p. 667.
^ Sherrington: Schiiefer'.s Text-book of Physiology. 1000, vol. 2, p. 874,
PARALYSES IN DOGS 111
of the fibers in a given root are about on a level with the superficial origin of that root from the cord. Sherrington^ has advanced
some evidence for this, which evidence is based partly on the
fact that after section through the cord just above a given anterior root, very little degeneration is to. be seen in the fibers of that
root, and partly on the results of direct stimulation of roots above
and below the place of section. Besides Sherrington's contribution important reports on the results of direct stimulation of roots
have been made by Bikeles and Gizelt, Langley,i° and Risien
Russel.i^ The subject has been studied in connection with the
formation of the lumbo-sacral plexus. The results agree fairly
well, the fibers constituting the main nerve trunks being said to
arise from the cord in the following descending order: crural,
obturator, gluteal, sciatic, tail and sphincters. The internal
popliteal fibers are, as a whole, placed higher than the external
popliteal. There is supposed to be considerable overlapping of
nuclei. Further than this longitudinal relationship, little infor-.
mation is obtainable by the method. Our results conform fairly
well to the above order except as regards to relative height of the
external popliteal and internal popliteal.
A second method is based upon the pathological findings in
human beings in such conditions where definite motor paralysis
were clinically under observation i- (infantile paralysis, tumors of
the cord, etc.) . The observations are, however, very fragmentary.
The third method consists either in the amputation of limbs
or parts of limbs, or in the excision of peripheral nerves, and
later studying the ganglion-cell changes to be observed in the
spinal cord. Valuable contributions have been those by Sano,^^
Van Gehuchten and Nelis,i^ Flatau,^^ Marinesco,^^ Bruce, ^^ and
» Sherrington: Journ. of Physiol., vol. 13, 1892, p. 621.
« Bikeles and Gizelt: Pfluger's Archiv, 1905, vol. 106, p. 43.
'"Langley: Journ. of Physiol., 1891, vol. 12, p. 347.
11 Risien Russel: Proceed. Royal Soc., 1894, vol. 54, p. 243.
1^ Wickmann: Die Riickenmark-nerven und ihre Segment-beziige, Berlin, 1901.
" Sano: Les localizations des functions motrices de la moelle epiniere, 1908.
" Van Gehuchten and Nelis: Jour. de. Neurol., 1898, p. 301.
15 Flatau: Archiv f. Anat. u. Physiol. Physiol. Abt., 1898, p. 112.
'"Marinesco: Revue Neurol., 1898, p. 483.
1' Bruce: Topographical atlas of spinal cord. 1901.
112 HENRY O. FEISS
Knape.^^ Knape is practically the only one of these who leans
toward the theory that cell groups represent collections of fibers
in peripheral nerves. Even he does not describe sharply circumscribed nuclei as representing these nerves. He let his animals
run a long time after excising the nerves, and before he studied
the cords, in several cases allowing an interval of almost five
years to intervene. His nuclei extend over more segments than
our own.
As to previous observations on sphincteric control, reliance
has usually been placed upon the stimulation of roots. ^^ According to most observers^"' 21. 22 h^q nerve supply affecting control
of micturition in dog and cat comes from two sources in the cord,
an upper from the 3d, 4th and 5th lumbar roots, and a lower
from the 2d and 3d sacral roots. Nerve fibers are sorted out
in the hypogastric plexus before they finally pass to the bladder
itself. According to Bechterew,-^ Sherrington, ^^ Langley and
, Anderson,25 and others, the lower source is especially important.
This does not conform to our localization for bladder control in
the 7th lumbar or 1st sacral segments.
Very much like the bladder, the rectum receives its nerve-supply
from two sources, 2*^ and from about the same spinal nerves. Moreover, as in the case of that organ, the sacral nerves are much more
important than the lumbar. Masius,^^ and Ott,^^ like ourselves,
place the center higher than the lower source given by the others.
18 Knape: Zieglcr's Beitrage. 1901, vol. 29, p. 251.
'^ Langendorff: Nagels Handbuch der Physiologie, vol. 4, 1st half, p. 350.
-" Nawrocki and Scabitschewsky: Pfltiger's Archiv, 1891, vol. 48, j). 335, vol.
49, p. 141.
" Budge: Zeitsch. f. rational med., 18G4, vol. 21, pp. 1 and 174.
22 C. C. Stewart: Amer. Jour, of Physiol., 1899, vol. 2, p. 182.
2' Bechterew: Functionen dor Nerven Centra, 1908, vol. 1, p. 292.
2^ Sherrington: Schaefcr's Text-book of Physiology, 1900, vol. 2, p. 874.
" Langley and Anderson: Jour, of Physiol., 1895, vol. 19, p. 71.
■• Starling: Schacfer's Text-book of Physiology, 1900, vol. 2, p. 336.
" Masius: Bull. Acad. Royal de Belgique, pp. G7, OS.
2« Ott: Jour, of Physiol., 1879, vol. 2, p. 54.
PARALYSES IN DOGS 113
The significance of cell-groups in the grey matter of the spinal cord
According to different authors, the cell-groups in the gray matter
of the cord are variously supposed to represent muscles, peripheral
nerves, primary metameres or movements (as in the cortex).
After a rather careful scrutiny of some of the literature, beside
that mentioned above, we feel that in the present state of our
knowledge, there is not sufficient evidence for any of these explanations. It is by no means certain that these cell-groups have
any physiologic significance whatever. According to Knape, as
above shown, and according to our own experiments, the findings
seemed to point somewhat toward the peripheral nerve theory.
Another piece of evidence for this theory is the fact that some of
the cranial nerves have their cells of origin grouped in fairly well
circumscribed nuclei. But neither is this analogy, nor the other
evidence which we have cited, of sufficient weight to carry conviction. If the grouping of cells in the cord is ever susceptible
of explanation, much further investigation will be required.
PART 3. NERVE FUSION ATTEMPTED IN THE CAUDAS AND THE
SCIATIC NERVES IN ANIMALS PARALYZED BY MECHANICAL LESIONS IN THE SPINAL CORD
This part of the research is based on eight cases, the only ones
in which the animals survived both the original spinal lesion and a
secondary 'fusion' done some time after they had reached permanent states in their paralyses.
The aim of the procedure
Nerve fusion, it has been stated, consists simply in uniting two
or more nerves by tying them together with absorbable ligatures.
In the preliminary report-^ the theoretical basis for this procedure
is given, the important point being that the direction of fibers
regenerating in scar is governed by conditions offered by the mass
of proliferated cells and nuclei which are here formed. As these
are laid down in all directions the new fibers which dev^elop in
the interstices of the cells must grow accordingly. Therefore it
28Feiss: Boston Medical and Surgical Journ., May 11, 1911.
114 HENRY O. FEISS
may be hoped that permanent changes in nerve pattern might
result, and if two or more nerves are joined, that the mechanical
attributes of the scar might cause fibers from fascicles of one
nerve to pass into those of another. Besides, as shown by
Perroncito,^" Bethe^^ and others, one might even hope for branching of some of the regenerating fibers, so that if certain tracts,
previously emptied by the paralysis, are entered by the new
branches, there might result not only a change in nerve pattern
but perhaps also a relative increase in the number of fibers. The
purpose of the ligature is thus seen — it not only brings the nerves
into physical apposition, but it also crushes them so as to cause
the scar to form. Being absorbable (cat-gut) it disappears of
itself. Compared with the older method of nerve crossing by
suture, the theoretical advantages are: (1), that no division of
nerves may be necessary; (2), that as many nerves as are in physical proximity may be included in the fusion; and (3), that change
of nerve pattern may be hoped for in the individual nerve, even
if no other unites with it.
Of special interest is the fact that in the cauda, at the region of
the interspace between the dural exits of the 5th and 6th lumbar
roots (dog) one may intradurally gather all the roots which supply
the hind limb and tail into a compact bundle, and fuse them in
the manner suggested above. In fact, by retracting the sensory
roots, the motor roots alone may be thus joined together.
Below are given summaries of experiments in which fusions
were attempted either in the cauda or in the sciatic nerves, some
months after primary lesions were produced. These lesions have
already been described (Part 2). The essential facts in the
secondary fusions are given in table 3.
Experimental data^
Experiment 64. Lesion, January 18, 1910. On April 27, 1910, residual paralysis (fig. 6) chiefly of left external poi:>liteal. On this date,
following operation, left sciatic exposed, and aft(T faradic stimulation"
2" Perroncito: Zicgler's Beitrage, 1007, vol. 42, p. 354.
" Hethc: Pflugei'.s Arohiv, 1907, vol. IIG, p. 3S.5.
■" All exposures of roots and nerves were miidv. under full ether aiuiesthesia.
'^ In all the experiments a du Hois coil with 10,000 windings of the secondary
and a two-pint Daniell cell in the primary current, were used.
PARALYSES IN DOGS
115
determining that there was no re.sponse in the external popliteal the two
pojjliteal.s (.sciatic) crushed with haemostat and tied together with three
cat-gut ligatures one-quarter inch apart. On August 19 (114 days
after fusion), same nerves exposed, and firm neuroma found at place of
fusion. Faradic stimulation of external popliteal showed flexion of
toes, but no extension. Internal popliteal responded normally. On
November 6 (193 days after fusion) similar responses and animal sacrificed. No cUnical improvement noted.
TABLE 3
O
o 2
2 ^
5
FUSION
RESULTS OF FOSION
^;
Eu »
o s
OS a
S SI
m B.
S X
Number of
days after
date of
lesion
Clinical
(functional)
Physiologic
(faradic)
Anatomic
(myelination)
64
Paw and
ankle
E. P.
97
Popliteals
Slight (?)
improvement
Negative
Some regeneration in and
below neuroma
69
Paw and
123
Popliteals
Worse than
Negative —
Some regener
ankle
before
Stumps not
a t i o n in
E. P.
united
peripheral
stump
78
Paw and
ankle
E. P.
129
Popliteals
No improvement
(death in
60 days)
No tests
Beginning regeneration
in neuroma.
None in E.
P. below neuroma.
65
Most of leg
99
Ant. roots
in Cauda
As before
Doubtful
Slight regeneration
70
Most of leg
124
Ant. roots
Worse than
Responses in
Fair regenera
in Cauda
before
roots and
nerves
tion below
neuroma
75
Most of log
122
Ant. roots
in Cauda
Worse than
before
No tests
Slight regeneration below
neuroma
68
Tail
85
Cauda-Sa
Fair im
Good
Some regener
cral and
prove
responses
ation in and
coccj^geal
ment
below neu
roots
roma
73
Tail
111
Cauda-Sa
Fair im
Fair
Some regener
crul and
prove
responses
ation in and
coccygeal
ment
below neu
roots
roma
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 2
116 HENKY O. FEISS
Anatomic report (In this and the following experiments, sections were
stained by Weigert-Pal and general methods) : Left sciatic above scar
showed normal fibers and some unusual patches of connective tissue.
Sections through midst of neuroma showed many small, and partially
myelinated fibers some in bundles and others scattered among the cells
of the scar. Scar dense and contains numerous nuclei. Popliteals
below scar show scattered fibers with large interspaces and myelination,
although not complete further advanced than in scar. Some large
areas where no fibers appear suggesting that sheaths emptied by lesion,
have not been filled.
Experiment 65. Lesion, January 19, 1910. On April 28, 1910,
residual paralysis (fig. 14) chiefly of left leg. On this date, following
operation: 6th and 7th arches removed, dura opened, cauda exposed.
Sensory roots lifted aside and such motor roots as lay in the field stimulated. No response except in tail. Motor roots fused with one catgut ligature and crushed with haemostat. Dura sewed. Wound closed
tight. No clinical improvement noted after operation. On September
26, 1910, stimulation of roots attempted with doubtful results. Animal sacrificed.
Anatomic report: Partial disappearance of anterior roots at region
of fusion. Some scar with only a few nerve fibers interwoven in it.
Roots peripheral to scar show greater numbers of fibers and myelination
further advanced.
Experiment 68. Lesion, March 17, 1910. On June 10, 1910, residual paralysis (fig. 22) chiefly of tail and slight weakness of dorsal flexion of right paw. On this date following operation: 6th lumbar arch
removed and all sacral and coccygeal roots (both anterior and posterior)
constituting cauda at this region, fused with two cat-gut ligatures.
No change noted after operation till in September or October, when tail
seemed to be moved better (figs. 26 and 27). Thereafter but little gain.
On November 30, 1910 (173 days after fusion), all roots divided and stimulated peripheral to fusion-neuroma and found to evoke tail movements.
Animal sacrificed.
Anatomic report: Place of fusion shows dense and knotty sear with
large numbers of cells running in all flirections. Among these, small
and partially myelinated nerve fibers have formed. Roots peripheral
to scar contain fibers Ijetter myelinated, some almost normal.
Experiment 69. Lesion, March 17, 1910. On July 18, residual partial paralysis (fig. 12) of muscles supplied by right external popliteal.
On this date following operation: right sciatic divided above bifurcation and immediately resutured. Then popliteals fused by usual method
with two cat-gut ligatures. (The object of the division was to promote
fibrillation at the; cut end of the central stump, before the fibrils entered
the regioii of fusion.) (Clinically dog became worse after the operation.
On December 19, 1910, nerves investigated under ether and the cut ends
of the sciatic were found ununited. Yet stimulation of popliteals below
neuroma evoked responses. Animal sacrificed.
Anatomic report: J'oplileals in fair states of regeneration.
PARALYSES IN DOGS 117
Experiment 70. Lesion IVIarch 18, 1910. On July 20 residual spastic parah'sis (fig. 18) of both legs. On this date operation similar to
that done on dog 65. The immediate result was fiaccidity of homolateral
paw. December 8, 1910, all roots which were involved in the fusion
scar divided and stimulated under ether. Leg movements evoked on
side of fusion, similar to those on other side. Popliteals stimulated and
responded to weak currents. Animal sacrificed.
Anatomic report: At region of fusion dense scar containing i^artially
myelinated fibers. Peripheral to scar, roots show myelination better
advanced.
Experiment 73. Lesion March 19, 1910. On July 8, 1910, residual
paralysis (fig. 24) confined to tail. On this date operation similar to
that done on dog 68. In September dog was wagging tail pretty well
and seemed to have more strength in it. On December 20, 1910, all
roots below fusion divided and stimulated, under ether, and tail responses
evoked. Animal sacrificed.
Anatomic report: Region of fusion showed dense, knotty scar infiltrated with nuclei, also a few fascicles of good filjers and some partially
myelinated fibers interwoven among the cells. At more caudal levels
regeneration quite advanced.
Experimeyit 75. Lesion April 12, 1910. On July 12, residual spastic
paralysis (fig. 16) of right leg, except for paw which was flaccid. On
this date operation on right anterior roots similar to those done in dogs
65 and 70. Clinical result completely negative. Death by accident,
November 20, 1910.
Anatomic report : In region of fusion, dense scar containing some faintly
myelinated fibers.
'Experiment 78. Lesion April 15, 1910. On August 22, 1910, residual paralysis (fig. 8) chiefly of right external popliteal. On this date
following operation: external popliteal divided and fused to internal
popliteal low down. Dog found dead, October 10, 1910.
Anatomic report: Right sciatic above fusion contained increased connective tissue spaces. At region of fusion dense scar with numerous
nuclei. New nerve fibers among these running in all directions. Some
regeneration in nerves below fusion.
Discussion
In the three dogs (Experiments 64, 78 and 69), in which the
popliteals were fused, there was no functional gain, although
there was anatomically some regeneration in all the nerves below
the scar. In one of these (78) death occurred before any functional result could be expected. In dog 69 where the sciatic was
sectioned higher up and the stumps failed to unite, the peripheral
stump must have made new central connections through small
fibers injured in the wound during the operation. The stim
118 HENRY O. FEISS
ulation tests in Experiment 64 could not be said to be positive
for the external popliteal. As to the other five dogs, the three
which had their anterior roots fused on one side could not be said
to show any functional gain, although two (Experiments 65 and
70) showed some response to faradic stimulation in the roots
below the fusion. Anatomically again, there was some regeneration.
The only animals in which functional improvement was suggested were dogs 68 and 73, both of which had paralyzed tails,
and therefore had the fusion done so as to include all the roots,
taking part in the innervation of that appendage. ^^ In both of
these, there also were signs of good regeneration, from the anatomical and physiological points of view. However, one could
not be positive that the functional return of power was due to
the fusion, because it took place so soon after. To help settle
this point we performed similar operations in the cauda of three
normal dogs. In these cases the tails were pretty well restored
in power by the end of three months. It is likely that this early
improvement is owing to the shortness of route between the nervecollectors of the tail and the roots from which these are formed.
As regards the whole question of the fusion of nerves, it is not
desirable, at the present time, to discuss it further on a basis of
the experiments above described, but, at some future time, after
becoming acquainted with conditions of regeneration after the
fusion of normal nerves, it is likely that these experiments will be
alluded to again.
In closing, I wish to acknowledge the assistance of Dr. R. H.
Bishop in the conduct of many of the experiments, and of Dr.
David Marine in the ])j'eparation and inter])retati()n of anatomical
material. I am especially indebted to Professoi- (Jeorge N.
Stewart, Directoi- of the Laboratory. He has made many important suggestions in the plan and details of the work, as well as
in the preparation of the manuscript.
Clevelaii.l, Ohio.
Scliuiii.iclicr: AiKil. llcflo iJciLiiij^c /iir Anal,, iiinl I'lnl u ickclmifisge.scluclite,
120 Ilcft., 1(10!).
PARALYSES IN DOGS
119
5
Fig. 1 Instiiinieiit used to produce lesions.
Fig. 2 Experiment 90; two days after lesion.
Fig. 3 Experiment 90; five days after lesion.
Fig. 4 Experiment 100; two days after lesion.
Fig. 5 Experiment 100; twenty-one days after lesion.
Fig. 6 Exijcriiiiciit (>1; niiifty-l'our d;iya niter lesion. Jjol't, no dorsal flexion
of paw and ankle ; direct stimulation of nerves showed E. P. practically all involved.
Fig. 7 In this and the following diagrams, the topography of the cord lesions
i.s indicated; fine stipple represents cavity; parallel line shading represents broken
down tissue; cross-hatching represents dense scar from dur.i; (lie heavy shading
in the circles, whicli ropre.senl roots, indicates the extcnl of involvomont at the
level shown; degenerations arc not rejjresented. f]']. J'..iii(l 1. I'. ^ inlcrniil nrul
external poplitcals respectively.]
120
Figs. 8 and 9 Experiment 78; ninety-one day.s after the lesion. Right, no
dorsal flexion of ankle and paw; weak extension of hip and knee; direct stimulation of nerves showed E. P. (right) all involved.
121
Eyper: 8Gj •
Root 3
11
Figs. 10 ;ind 11 I'lxpiTinicnl S(;; scvciil \-()iic days aflcr lesion; condilion little
changed two to throe inontlis later, viz.: right, no dorsal flexion of i)a\v and ankle;
weak plantar flexion of toes; knee quite weak in extension; hip usually held flexed
and also weak, left, stronger than right; dorsal flexion of paw and ankle gone;
hip and knee slightly weak, liefore killing, direct stiniulation of nerves showed
Right, /. I'., slight response in toes; no inovenieiil in ankle. /','. /'., lU) response;
left, /. I'., good response in foes; good n^sponse in ankle; A'. /'., no icspon.se.
122
Exper 69
Root 4 '-'
5.'
5L !\\
- i 6L
tfi-i
'7;; IS
<i L
15-^ Le/el
2nj
R
31-^ " AXb
4 th ..
G
VG
13
7'/ '--^
Figs. 12 and 13 Experiment 69; eighty-five daj^s after lesion. Right, dorsal
flexion of paw and ankle weak.
123
Exper G5 If]
Roof 4
Figs. 14 and lo. Kxpcriiiicnt 05; iiiiid y-tliroo days after lesion. Left, bad
control of paw and ankle; knee flex(M|; hip contraeted and extension lessened.
Right, flexion of hip weak (so (hal she occasionally (lr;ii;s leu); weak i)ower in
extension of knee.
124
17
Figs. 16 and 17 Experiment 75; ninety-four days after lesion. Right, no control except in flexion of hip; leg held under her, being flexed and adducted at
hip; knee and ankle held straight and stiff; paw probabh* paralyzed and is held
flaccid; glutei and hamstrings weak; quadriceps partially gone but contracted.
12.-)
l'"ig.s. 18 and 1!( Ivxix'riiiicnt 7(); one Imiidrcd ;inil twcaly-tlircc days after
lesion. Poor control of pelvis, liii).s, knees, aidvlcs and paws, but for the mostpart,
not an atonic, flaccid paiulysi.s. All joints ;ii-e lield pennanontly flexed to about
normal angles, except the hips wliieh are more extended tli.tii usual; spine bent
convexlybackwarfl. On both sides erector spinac, glutei and cpiadriceps all weak;
hamstrings fairly good; paws turn under occasionally; drags legs in i)osition
d(!scribe(j.
126
\ 21
I'll r^
Figs. 20 and 21 Experiment 72; sixty days after lesion. Practically no control
of paws, ankles, knees, hips and pelvis.
127
Figs. 22 and 23 Kxpfrirncnt fiS; sixly-two days after lesion. 'I'ail,
paralyzcfl; sonu^ jiowcr in toot. Hitiid, dorsal flexion of paw weak.
128
mostly
25
Figs. 24 and 25 Experiment 73; sixty days after lesion. Tail, mostly paralyzed; moves root a little.
129
Fig. 26 Kxijcrimont 68; one liundied and thirty-nine days after lesion; fiftyfour days after fusion. Practically no control of tail.
Fig. 27 Experiment 6S; 1 wo hundred and nine; days after lesion; one hundred
and twenty-four days after fusion; showing extent of control of tail in lifting at
this date.
i;]()
THE INFLUENCE OF AGE, SEX, WEIGHT AND RELATIONSHIP UPON THE NUMBER OF MEDULLATED
NERVE FIBERS AND ON THE SIZE OF THE LARGEST
FIBERS IN THE VENTRAL ROOT OF THE SECOND
CERVICAL NERVE OF THE ALBINO RAT
ELIZABETH HOPKINS DUNN
Frovi the Hull Laboratory of Anatomy, The University of Chicago
SIX FIGURES
So much has been pubhshed regarding the growth of the medullated nerve fiber that an explanatory word may be permissible
on offering a paper which duplicates in many particulars the
findings of other investigators.
The collection of the data presented here was suggested in
1903 by an examination of the control, or normal, material used
by Dr. S. W. Ranson for his study of the spinal ganglion. Of the
sectioned material, that for five rats of the thirty-one here reported was generously furnished by Dr. Ranson. In examining
that material the salient feature was, to me, the increase in size
of the medullated nerve fibers in the older rats, and it seemed
desirable to ascertain if possible what conditions other than age
might influence the size of these fibers. This point seems to
have attracted other interest, since in 1906 Dr. Boughton
published important data regarding the increase in size with age
and weight of the medullated nerve fibers of the oculo-motor
nerve in the albino rat and in the cat from a mixed series of males
and females.
While the chief point of my inquiry was so admirably elucidated
b}^ Dr. Boughton's paper, there seemed to be place for the more
extended study with defined categories which I had undertaken.
Inquiry was made before continuing the work as to the existence
131
THE JOURNAL Or COMPARATIVE NEUROLOGY, VOL. 22, NO. 2
132 ELIZABETH HOPKINS DUNN
of any further duplicating studies. When it was learned later
that Mrs. M. H. S. Hayes had a considerable series of counts of the
ventral root nerve fibers of the second cervical nerve for the albino
rat, postponement of publication was made for more than two
years, but as her material has not been published it has seemed
expedient to present my own findings with all due. apologies to
others.
With age as the constant factor in each group it seemed wise
to vary the other factors which might determine the size of the
largest nerve fibers. The additional factors selected were sex,
body size as shown by extremes of weight within the limits of
health, and relationship as shown by conditions within the same
litter or in different litters. To these ends seven groups of rats
were selected ranging in age from seven days to two hundred and
seventy days, or nine months. These two limits were determined
upon, the first because technical difficulties made accuracy in,
measurement among younger rats rather uncertain and the
second because it had been found difficult to maintain good health
and normal weight among laboratory rats after nine months of
life. Each one of these seven groups was made up of four rats
of the same age but of as widely varying weights as could be
secured among healthy animals. The emphasis was laid upon the
selection of light and heavy females, light and heavy males, thus
including two females and two males in each group. Further
information concerning conditions within and without the litter
was secured by selecting certain groups from one litter and other
groups from scattered individuals. The four rats of seven days,
three of fourteen days and the one rat of one hundred and thirtyeight days are of one litter. The four rats of the group at thirtysix days are of one litter. The three rats of seventy-five days are
of one litter. The four rats of the group at two hundred and
seventy days are of one litter.
To this series of seven groups was added a group of aged rats,
three males, of widely varying weights but not in good health.
These rats were about six hundred and forty days of age.
As previously stated, the medullated nerve fibers of the ventral
root of the second cervical nerve were selected for study and for
SECOND CERVICAL NERVE OF THE RAT 133
the purpose of uniformity the fixed point of section was opposite
the spinal ganglion and central to the fusion of the two roots.
The methods of preparation of the material were those used for
the enumerations and measurements in the leopard frog, (Dunn,
'00, '02, '09) and differed but shghtly from those of Boughton,
('06) Donaldson and Hoke ('05) and those of other investigators
with whose findings comparison will be made. The nerve roots,
ganglion and a portion of the nerve were fixed and stained unseparated in a one per cent solution of osmic acid, imbedded in paraffin, cut to a thickness of 4 micra and mounted serially.
The counts were made by the aid of an ocular net, and the
measurements with an ocular micrometer, using an oil immersion
lense at a magnification such that ten of the subdivisions of the
ocular micrometer equalled one of the stage micrometer, or one
one-hundredth of a millimeter. One division equalled 1 micron.
This magnification facilitated greatly the final computations which
were at best very tedious and required the closest control to eliminate the chances for error.
In selecting the nerve fibers for measurement, the entire section was surveyed and. the largest fibers methodically selected.
Each fiber was measured in two diameters, and its axis cyUnder
immediately measured in the same diameters.
The counting was done in daylight and the measurements taken
under an oil immersion lense by the aid of an electric microscopic
bulb of thirty-two candle power.
It was at first intended to select a variable number of nerve
fibers for measurement, making the number proportional to the
number of medullated nerve fibers in the section. But this plan
was abandoned in favor of that of a fixed number which showed
more accurately the increase in size at successive ages. The
number fixed upon was ten. The results of this examination are
found in tables 1 and 2.
Table 1 shows individual by individual, the age, the sex, the
weight in grams, and the number of medullated nerve fibers in
the ventral root of the second cervical nerve. Then for the ten
largest medullated nerve fibers, the average diameter in micra,
and the average area *in square micra for the fibers, and the
134
ELIZABETH HOPKINS DUNN
TABLE 1
Records from measurements on the ten largest nerve fibers in the ventral roots of the
second cervical nerve in a number of albino rats
-i
ft
a
WEIGHT
« o
D fa
TEN LARGEST FIBERS
THEIR AXISCYLINDERS
.Average
diameter
Average
area
DM
Average diameter
Average
area
O W
■
Grams
A...
7
Female
8.25
368
4.60
16.61
3.60
10.18
1 : 1.63
A...
7
Female
8.93
368
4.75
17.80
3.75
11.00
1 : 1.62
A...
7
Male
8.90
372
5.05
19.95
4.05
12.82
1 :1.56
A...
7
Male
9.75
360
5.60
24,63
4.55
15.07
1 :1.63
A...
14
Female
19.98
518
7.05
38.93
4.85
18.40
1
2. OB
B...
14
Female
21.85
566
6.95
38.04
4.75
17.79
■ 1
2.14
A...
14
Male
20.73
536
6.60
34.13
4.50
15.90
1
2.21
A...
14
Male
21.93
594
6.35
31.59
4.30
14.52
1
2.19
C...
36
Female
39.17
651
9.35
68.81
5.80
26.42
1
- 2.38
C...
36
Female
45.30
654
10.55
87.58
6.75
35.89
1
2.44
c...
36
Male
31.20
536
10.36
84.30
6.50
33.18
1
2.51
c...
36
Male
52.65
689
9.90
76.98
6.20
30.19
1
2.55
D...
75
Female
130.31
505
12.15
115.75
7.90
49.01
1
2.36
D...
75
Female
143.10
615
12.10
114.99
8.00
50.26
1
2.29
D...
75
Male
149.40
609
12.15
116.13
8.20
52.81
1
2.20
E...
74
Male
189.70
726
12.25
117.67
8.20
52.81
1
2.23
F...
133
Female
161.00
634
12.70
126.68
8.25
53.58
1 :2.18
G. ..
133
Female
167.51
731
13.60
145.27
9.10
65.03
1 :2.23
A...
138
Male
260.00
680
13.16
133.96
8.84
61.37
1 :2.18
H...
132
Male
274.00
569
13.70
148.04
9.10
65.03
1 :2.27
I....
180
Female
200.00
510
14.55
166.50
9.80
75.43
1
2.20
J...
180
Female
225.00
526
14.75
171.11
9.85
76.36
1
2.24
K...
180
Male
227.60
546
15.45
187.23
10.65
88.91
1
2.11
L...
180
Male
302.00
662
16.55
215.38
11.70
107.51
1
2.00
M ..
270
Female
165.85
698
18.20
260.16
13.10
134.78
1 : 1.94
M ..
270
Female
187.96
853
18.25
261.87
12.95
131.92
1 : 1.98
M ..
270
Male
330.68
576
16.25
207.65
11.30
100.28
1 :2.06
M..
270
Male
349.41
658
16.95
225.91
12.05
113.85
1 : 1.98
N'..
Aged
Male
210.00
901
14.85
173.43
10.50
86.59
1
2.00
0»..
Aged
Male
379.40
934
15.00
176.69
10.00
78. M
1 .
2.25
Pi ..
Aged
Male
414.00
758
14.35
161.96
9.40
69.40
1 .
2.33
' These aged rats were about 640 days old. They wcro killcil in 1903, 1904 and
1907.
SECOND CERVICAL NERVE OF THE RAT
135
average diameter and the average area for their axis cyhnders;
and, in the final column, the ratio of the area of the axis cyhnder
to the area of the entire fiber.
TABLE 2
Averages for the enumerations and measurements for the groups of albino rats
specified in table 1
7 days
Two females.
Two males. . .
Both
14 days
Two females.
Two males. . .
Both
36 days ■
Two females.
Two males. . .
Both
75 days
Two females.
Two males. . .
Both
132 days
Two females.
Two males. . .
Both
180 days
Two females.
Two males. . .
Both
270 days
Two females.
Two males. . .
Both
640 days
3 males
Grams
8.59
9.33
8.96
20.92
21.33
21.12
42.24
41.93
42.08
136.70
169.55
153.13
164.26
267.00
215.63
212.50
264.80
238.65
176.91
340.05
258.48
334.47
NUMBER
FIBERS
368
366
367
542
565
554
653
613
633
560
668
614
683
625
655
518
609
564
776
617
697
864
AVERAGE AREA
TEN LARGEST
FIBERS
17.21
22.29
19.75
38.48
32.86
35.67
78.19
80.64
79.42
115.37
116.90
116.14
135.98
141.00
138.49
-168.83
201.30
185.06
261.02
216.78
238.90
170.69
AVERAGE AREA
THEIR AXES
10.59
13.94
12.27
18.10
15.21
16.65
31.16
31.69
31.42
49.63
52,81
51.22
59.31
63.20
61.26
75.89
98.21
87.05
133.35
107.07
120.21
78.18
RATIO OF
AREAS
1.62
1.60
1.61
2.13
2.16
2 14
1 :2.51
1 :2.54
1 :2.53
1 :2 32
1 :2.21
1 :2.27
2.29
2.23
2.26
- 2.22
- 2.02
- 2.12
1 96
2.02
1.99
1 :2.19
136
ELIZABETH HOPKINS DUNN
Table 2 introduces the averages for the groups of rats, first
according to sex, and finally as a whole. It shows the average
weight, the average number of medullated nerve fibers, the average areas of the largest nerve fibers in square micra, the average
areas of their axis cylinders, and the ratio of these averages.
It may be of interest to show how the individual rats of the
selected series differ from such averages as have been estabhshed
already for the weight-age complex. In a joint paper by Donaldson, Watson, and Dunn ('06) certain averages and extremes of
weight by age were published, upon which I have drawn for a
series comparable with the present series. These data are presented in table 3 and are followed in table 4 by a compilation of
the ages and weights of the rats of the present study.
TABLE 3
MALES
FEMALES
D.'VYS
Lightest
Heaviest
Average
Lightest
Heaviest
Average
7
7.3
12.7
9.2
7.5
11.8
8.7
14
14.0
17.6
15.2
13.5
18.1
15.6
37
28.5
48.0
37.8
29.8
47.4
39.5
76
89.8
157.5
121.3
89.6
131.6
110.4
131
132.4
249.2
202.5
151.2
214.7
178.6
178
167.9
291.2
239.4
153.0
215.0
191.7
256
190.5
310.0
265.4
TABLE i
MALES
FEMALES
DATS
Lightest
Heaviest
Lightest
Heaviest
7
8.90
9.75
8.25
8.93
14
20.73
21.93
19.98
21.85
36
31.20
52.65
39.17
45.30
75
149.40
189.70
130.31
143.10
132
260.00
274.00
101.00
167.51
180
227.60
302.00
200.00
225.00
270
330.68
349.41
165.85
187.96
SECOND CERVICAL NERVE OF THE RAT 137
A comparison of the records for the approximate ages shows
that, while the individuals of the present inquiry, are not the
lightest or the heaviest which might be obtained, they vary in a
satisfactory degree from the averages given for males and females
of comparable ages. I am not able to state the relationships of
the Watson groups of rats but in my own groups of the younger
rats a number of litters was included for each age.
The young of any given litter tend at birth to be of like weights
and, so far as the argument can be drawn from records of the
members of one litter, such related rats if differing initially in
weight tend to approach each other in weight as growth goes on,
if the conditions of growth are favorable (Dunn, '08).
Donaldson ('08, p. 353) says, "It is a familiar fact that rats
even of the same litter and reared together grow very differently
and therefore at the same age may have widely different body
weights." Unfortunately we have no published data to show the
initial body weight for related rats which differ so greatly at
maturity. It appears, however, that unrelated rats and those
reared under different conditions exhibit less uniformity of growth.
The present findings suggest that these variations from the average may make themselves apparent in the nervous system as
well as in the body weight. This is shown in the group at one
hundred and eighty days of unrelated rats which, while fitting
into the scheme for body weight, give numbers of fibers which are
less than might be expected.
In all the findings which refer to weight the females must be
considered separately from the males, at least after sexual maturity, since the growth curves for body weight differ greatly. For
the curves showing this, reference may be made to Donaldson's
papers, chiefly the collaboration with Watson and Dunn ('06).
The body weight for the male rat increases for a longer period than
that for the female and the average body weight for the adult
male is considerably greater than that for the adult female of the
same age.
The findings for this series of albino rats group themselves under
two heads, first, the factors influencing the number of medullated
nerve fibers, and second, those influencing the size of the nerve
138. ELIZABETH HOPKINS DUNN
fibers. The records for the individual rats are to be found in
table 1. For the group aV-erages table 2 must be consulted. Of
the figures fig. 1 gives in C a curve based upon the averages of the
groups for the body weight-age comparison, and in curves B and
A the comparison of age with the size of the largest fibers and of
their axis cylinders. Fig. 2 gives two curves related directly to
the number of medullated nerve fibers. Curve D has been plotted
for the fiber-age complex, and Curve E for group-weight averages
and number of fibers. Both curves of fig. 2 show considerable
irregularity in the later stages of growth. There is shown, however, a tendency for the number of medullated nerve fibers to increase in relation to both age and weight. The curves for the
two are quite different, since the increments of age are daily
periods, while the body weight is laid on chiefly during early life,
as is shown by Curve C, fig. 1, by which two-thirds of the maximum average body weight is found to be present at one hundred
and eighty days of life.
THE NUMBER OF MEDULLATED NERVE FIBERS
It is a difficult matter to estimate the direct relation of the number of medullated nerve fibers in the ventral root of the second
spinal nerve in the albino rat to the body weight if the attempt to
do so is made to the exclusion of the age factor. Especially is
this true in the present series in which the extremes of weight at
definite ages have been selected. So the attention has been directed to the variations to be observed within the group of one age.
This number-weight relation must be considered for the sexes
separately. If this is done the statement may be made that of
two female rats of the same age or two male rats of the same age
the heavier rat tends to have the greater number of medullated
nerve fibers. This is especially noticeable when the compared
rats are of the sam(^ litter. Unrelated rats are more likely to vary
from this rule. This finding in regard to weight corroborates that
of Mrs. M. H. S. Hayes in her unfinished work quoted by Hatai
('08, p. 154) with the added statement that this rule applies to
the sexes separately.
SECOND CERVICAL NERVE OF THE RAT
139
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l'"ig. 2 D is plotted to show the averages of the number of fil)crs for the four
rats of each group, at the ages studied. E is plotted to show the same averages
of numbers in relation to the averages of body weight at the same ages.
140
SECOND CERVICAL NERVE OF THE RAT 141
Our findings seem to show that age has more influence on the
number of medullated nerve fibers than has weight. In this
regard our records disagree with the conclusion of Boughton ('06)
for the oculomotor nerve of the albino rat. Reference to individual records in table 1 shows very definitely that there is no such
relationship between body weight and the number of medullated
nerve fibers that two rats of different ages but the same body
weight will be more likely to have the same number of medullated
nerve fibers in the ventral roots of the second spinal nerve than
those of the same age but different body weights.
The statement also seems justifiable that rats of like age and of
one litter tend to have the same number of medullated nerve fibers.
Curve E,fig. 2, has been plotted to show the relation of the averages for groups of rats of given ages to the averages for the number of their nerve fibers, but as this curve introduces the age factor
in addition to that of weight, it will be discussed in the following
section.
A considerable increase in the number of medullated nerve
fibers occurs during the early life of the albino rat. This was
noted by Hatai ('03) for the ventral roots of the sixth cervical,
the fourth thoracic and the second lumbar spinal nerves, and by
Boughton ('06) for the oculomotor cerebral nerve. In the second
spinal nerve the increase seems to be checked at an earlier period
than in the regions mentioned by Hatai. After the thirty-sixth
day of our series, (table 2 and fig. 2) there is no uniform increase
in the number of medullated nerve fibers, although the increments
of age are considerable.
Hatai ('03) using the criterion of body weight, argued that the
increase in number among the ventral root fibers continued to a
later period. His maximum of weight was 264.3 grams, which
might correspond to that of one of our one hundred and thirtytwo day rats. Hatai's conclusions were based on the findings
from one rat of each weight, age and sex not noted.
Boughton ('06) while noting age, weight and sex in his series
for the oculomotor nerve, did not select his material systematically
with respect to these factors. He obtained the maximum number of medullated nerve fibers in a male of one hundred and thir
142 ELIZABETH HOPKINS DUNN
teen days and with a body weight of 278 grams. However, his
curve immediately drops to a number not exceeding by one fib3r
the record for a male of seventy-seven days and 213 grams body
weight. Tozer and Sherrington ('10) argue that the oculomotor
is a mixed nerve.
Ranson ('08) made a few records for the number of ventral
root medullated nerve fibers of the second cervical nerve in the
albino rat in order to show the ratio of ventral to dorsal root
nerve fibers. While his records for the dorsal roots begin with
twelve day rats his counts for the ventral root fibers are only for
seventy-two day and six month rats. The level of the count, the
weight and sex of the rat are not stated.
His records for the dorsal root fibers give no stage between
twelve and seventy-two days but show a marked increase in
number at the later age. Of the ventral root fibers the average
number of fibers for four seventy-two day rats is six hundred
and thirty-two while that for two six month rats is seven hundred
and thirty-six fibers. My own averages for seventy-five day rats
and nine month rats give six hundred and fourteen fibers for
seventy-five days against six hundred and ninety-seven fibers
for the nine month rats.
Ranson's records then are comparable with those presented
now and together they show that in regard to the second spinal
nerve of the albino rat the number of medullated nerve fibers in
both the dorsal and ventral nerve roots increases during the life
of the individual but that the greatest increase occurs before the
sexual maturity or so-called puberty of the animal.
More than this, if comparison between Ranson's records for
the dorsal roots and my own records for the ventral roots of other
individuals is permissible, the statement is possible that the increase in number is relatively greater and extends over a longer
time among the dorsal root nerve fibers than among the ventral
root nerve fibers. The functional significance of this finding is
not so great as it would be if the counts for the dorsal root fibers
had been made peripheral to the ganglion when the fibers directly
innervating sensory elements would have beeA counted. As it
is, the records are for processes central to the ganglion and ending
SECOND CERVICAL NERVE OF THE RAT 143
in the central nervous system. More than this they are upon
individuals other than those from which the ventral root fiber
records were made. Comparable records may yet be secured for
the material upon which the present report is made. The plane
of the section which was necessary to make measurements on the
ventral roots peripheral to the ganglia reliable made similar
measurements upon the dorsal roots unreliable. If some control
for the measurements can be devised, the counts will also be made.
Whatever may be the significance of the presence of the added
fibers the determination of the time and manner of their appearance must be of importance.
The albino rat becomes sexually mature about the beginning of
the third month of extra-uterine life, or' about the seventieth day,
but its increase in body weight may continue, to the end of the
second year of life. According to the present records the average
daily increase in weight between the ages of seven and fourteen
days is 1.74 grams, and the average daily fiber increase is twentyseven fibers. The average daily increase between fourteeen days
and thirty-six days is 0.95 grams and 3.6 fibers. The increments of age and weight are too great to establish these averages
as final, but they undoubtedly show the general growth relations.
The rate of increase in the number of medullated nerve fibers,
in essential agreement with Hatai ('03) and Boughton ('06)
diminishes with age. In our series the fourteen day period marks
the greatest increase.
That such an increase in the number of medullated nerve fibers
occurs in other animals has been shown by Boughton ('06) for
the cat and suggested by Willems ('11) for the rabbit. Boughton
('06) used a mother cat and her five kittens, two males and three
females. An increase in the number of medullated nerve fibers
of the oculomotor nerve is shown among the kittens from one day
to one hundred and eighty-two days, with the exception of the
female at ten days, but the mother cat at thirteen years has a
number of fibers not quite equal to that of the kitten of fifty-six
days.
Willems' records ('11) were offered to show the relation of large
and small nerve fibers in the portio minor of the fifth cerebral
144 ELIZABETH HOPKINS DUNN
nerve and its branches in various adult rabbits but, unfortunately
for comparison with other records, do not state the age or sex of
the animal. There is shown however in his table 4 (p. 143) a
variation in the total number of medullated nerve fibers in the
motor portion of the fifth cerebral nerve which might indicate the
influence of an age factor.
It would seem from the present more extended series from albino
rats that the increase in the number of medullated nerve fibers
practically ceases with the attainment of the adult condition and
that the presence of an individually greater number after that
period is dependent upon some factor determining the number to
be supphed to the adult body and is not likely to be due to the
maturing of immature elements in the nervous system as it seems
to be at the earlier ages.
This increase in number of medullated nerve fibers with the
increase in weight and age may have several interpretations.
When it appears as a condition most marked during the period of
rapid growth, it may well seem to be associated w4th the increase
of the number of body elements which must be innervated. During the same period, or more naturally later, it may be dependent
upon an increased innervation of already innervated material.
Our data as regards the number of innervated peripheral elements either sensory or motor are extremely limited.
Intimately bound up with this question is that of the splitting
of peripheral nerve fibers, and no absolute correlation between the
number of nerve fibers in the spinal roots and the number of
peripheral innervated elements can be made with our existing
knowledge.
It would appear in general that the increase in size of the immature body is accomplished by the increase in both number and
size of the individual elements, while that of the mature body is
rather due to increase in size of the already formed elements.
Bough ton's TOO) findings lead him to state that after the initial
laying down of nerve fibers the added fibers never attain the size
of the earlier formed fibers, and the added fibers must be small
fibers. Under this interpretation size is determined by age. and
SECOND CERVICAL NERVE OF THE RAT 145
these additional fibers whatever their function are determined
by the time of their appearance to be small fibers.
This phase of the significance of the added fibers is so bound up
with the discussion of size that we may consider it more readily
under that topic.
SIZE OF THE MEDULLATED NERVE FIBERS
If the period preceding puberty marks the time of the chief
increase in the number of medullated nerve fibers, it has no such
notable relation to the increase in size of the medullated nerve
fibers, whicji continues at least to the ninth month. This is
clearly indicated in table 2, which gives the average areas in
square micra for the ten largest fibers of four individuals in each
group. In this table, and in fig. 1, curve B, an unbroken increase
occurs for our averages from the seven day group to the two hundred and seventy day group. A somewhat similar increase
occurs in the areas of the axis cylinders of the same fibers, showing
that the integral portion of the nerve cell increases in size during
health with increasing age at least to the ninth month of life.
The ratio of the average for the axis cylinder and for the entire
fiber (table 2) gives some interesting information as to the growth
of the medullary sheath. Using the average area of the axis
cylinder as the unit, at seven days the area of the entire fiber is
about one and one-half times that of the axis cylinder, that is the
medullary sheath has half the area of the axis cylinder. At the
succeeding stages of body growth to the two hundred and seventy
day period the medullary sheath is thicker than the axis cylinder.
The greatest relative thickness of the medullary sheath appears
in our series at the thirty-sixth day when, contrasted with the
unit area of the axis cylinder, the area of the medullary sheath
is 1.47. From this age there appears a readjustment in the growth
of the two, until at nine months the ratio is 1 : 0.99 or the one to
one relation of the normal adult (Donaldson and Hoke, '05).
Among the members of our group of aged and infirm male rats
the nerve fiber is affected in both axis cylinder and medullary
sheath. The average area of the entire fiber and of the axis cylin
146 ELIZABETH HOPKINS DUNN
der is considerably decreased. The axis cylinder is the more
affected so that the ratio approximates that of a fourteen day rat
or a hundred and eighty day rat, in which the medullary sheath
has a slightly greater area than has the axis cylinder.
The curves for the averages have been plotted in fig. 1, Curves
A and B. At seven days Curve A begins at 12 square micra and
Curve 5 at 17 sq re micra. As age increases the curves diverge
until at two hundred and seventy days the fiber is twice the size
of the axis cylinder. In old age, six hundred and forty days, the
axis cylinder has an average area of 78 square micra, while that of
the entire fiber is 171 square micra, showing a distinct shrinkage
in both axis cylinder and medullary sheath. *
The comparison of the curves for the nerve fiber and for its
axis cylinder with the curve for the body weight of the same animals is full of interest. Curve C has been plotted in the same
figure to show the relation of the body weights of the groups to
their age.
From this comparison we see that the size of the largest nerve
fibers increases more rapidly than the weight of the body until the
thirty-sixth day. From the thirty-sixth to the seventy-fifth day
or until puberty the body growth is very rapid, overshadowing
that of the nerve fiber. This disporportional growth of the body
continues until about the one hundred and thirty-fifth day. At
that age the body has acquired two-thirds of its ultimate size,
while the largest nerve fibers have acquired only a little more than
one-half of their ultimate size. The growth of the nerve fibers
from the one hundred and thirty-fifth day is more rapid than the
body growth, so that the curves approach one another at the two
hundred and seventieth day. At six hundred and forty days, or
old age, the curves are widely separated, due both to the increased
weight of the body and to the decreased size of the nerve fibers.
It may be well to discuss more fully the question of size as
related to all the nerve fibers.
Measurements have been made upon the largest nerve fibers
for convenience and for accuracy. To those who have made the
attempt, the difficulty of making such measurements with the
ocular micrometer need not be emphasized. The difficulty of this
SECOND CERVICAL NERVE OF THE RAT 147
series was considerably increased by the handling of very young
material.
These measurements prove the increase in the size of the largest
medullated nerve fibers, but that the increase is not confined to
the largest fibers is evident to one making even a casual study of
0-0 O
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Fig. 3 Camera lucida drawings by A. B. Stredain at table level, ocular 8, objective 8, Zeiss, showing typical areas from the ventral roots of the second cervical
nerve of three male rats of one litter. A at seven days, body weight 8.9 grams;
B at fourteen days, body weight 21.93 grams; C at one hundred and thirty-eight
days, body weight 260 grams.
Po9
D E
Fig. 4 Camera lucida drawings, at same magnification as those of fig. 3, showing typical areas from the ventral root o^the second cervical nerve of two male
rats. D at 270 days, body weight 349 grams; E at 640 days, body weight 414 grams.
the material. Fig. 3 was drawn by camera lucida to include
typical areas from the ventral roots of the second cervical nerves
of three male rats from one litter. A at seven days, B at fourteen
days and C at one hundred and thirty-eight days. Fig. 4 gives
drawings at the same magnification from two additional male rats,
D at two hundred and seventy days, and E at six hundred and
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22. NO. 2
148 ELIZfliBETH HOPKINS DUNN
forty days. The variation in size is too obvious to need further
comment. E shows the decrease in size among the old rats.
The increase in size is apparent among the majority of the fibers
and may include all the fibers. Nevertheless some of the medullated nerve fibers may appear early and not continue their growth
over the usual time or may grow more slowly. Small fibers may
be destined to be small fibers from their first appearance.
Boughton ('06) made an attempt to classify the medullated
fibers of the oculomotor nerve into 'large' fibers and 'small'
fibers. One is somewhat puzzed regarding his method. According to his table 1, Boughton entered all the fibers present at eleven
days as ' large' fibers, noting the addition of 'small' fibers at later
ages. In his discussion of method (p. 156) he states that all his
sections were photographed at the same magnification and only
those fibers distinctly recognizable at that magnification were
entered as 'large' fibers. If the material was at all comparable
to that of the present investigation a magnification which would
show all the fibers at the youngest period would show all the fibers
at all the other periods. Our fig. 3 proves this.
The oculomotor nerve carries a considerable number of small
medullated nerve fibers as viscero-motor fibers to the ciliary
ganglion (Apolant, '96, p. 664). The presence of such fibers
may account for the large number of small fibers found by Boughton ('06) in the oculomotor nerve of the albino rat. In such a
group of nerve fibers, which plainly differs functionally from the
somatic fibers, a distinct difference in size would be difficult to
interpret alone from the standpoint of age of the fibers. All
viscero-motor medullated nerve fibers have been recognized as
small fibers. This was early stated by Gaskell ('86) and Langley
('96) and corroborated by mahy more recent investigators It
is possible that these fibers are later in medullation than those
passing to the body muscles, but they may not grow so rapidly
as do the somatic motor fibers.
Further, if we have in the third nerve which has been considered
a purely motor nerve, a mixed nerve as Tozer and Sherrington
('10) have argued, the interpretation of Boughton 's findings, has
an added complication as both efferent and afferent fibers would
SECOND CERVICAL NERVE OF THE RAT 149
be included. Such an interpretation has been given to the function of the ventral roots by Kidd ('11) and others. I have
unpublished a note on the presence of medullated nerve fibers
in the ventral roots of the spinal nerves in the leopard frog, which
from the direction of their degeneration seem to have their cells
of origin in the dorsal root ganglia. It may be then that in no
nerve or spinal root are we dealing with unmixed fibers. The
relative number of efferent fibers seems greater in the second
cervical nerve than in any of those previously considered. Roth
('05) states as an argument in proof of the visceral character of the
eleventh cerebral nerve that in the rat the ventral roots above the
sixth cervical have a small number of small medullated nerve
fibers, and that the second cervical nerve has in its rami communicantes few or no small medullated nerve fibers.
Willems ('11) has discussed the question of the size of medullated nerve fibers quite fully giving prominence to three theories
and introducing one of his own based on the differences in size
found among the branches distributed to various muscles from the
efferent portion of the fifth cerebral nerve in the rabbit. Quoting
from page 203, Nous pensons done que I'individualite des nerfs
a son origine principalement dans la differente valeur de I'accroissement secondaire pour chaque muscle."
It has seemed to the writer that the propounders of these socalled theories as set forth by Willems have not attempted to put
forth an all embracing theory, but have each one been attempting
to define factors which may influence the size of the medullated
nerve fiber. Each one has noted conditions which have run parallel with size and have been piling up evidence bit by bit. At the
present moment it seems most probable that the size of the medullated nerve fibers must be interpretated finally as due to a combination of causes, and I anticipate that all the bits of information
will be wrought into a complex mosaic when the final illuminating
word can be said. One can readily see that in regard to size the
neurones may appear in successive crops so that the earlier crop
may have a greater size, according to Boughton's and Donaldson's attractive theory, while at the same time these successive
crops have definite functional values which in turn may be influ
150 ELIZABETH HOPKINS DUNN
enced by the richness of the fiber branching, by the size of the
innervated elements, by the frequency of their use, or possibly,
if neurofibrils are the conducting elements, by the number or size
of the neurofibrils. However this may be, we must be grateful
for every attempt to delimit the problem, while admitting that
much further information is desirable.
Increase in size is indeed a matter of growth, and it is extremely
confusing to the problem that age plays so large a part in determining the actual and possibly the relative size of the medullated
nerve fibers. It would appear that the next step in the interpretation involves the accumulation of a mass of data regarding the
direct relation of the size of the nerve fibers to the tissues innervated and much further information as to the relation of these
successively appearing fibers to the peripheral structures. The
latter involves a study of the axonic relations to the periphery and
the time of medullation of these axones.
My own findings (Dunn, '02 and '09) on the distribution of the
medullated nerve fibers to the segments of the leg of the leopard
frog suggest that difference in time of outgrowth from the central
nervous system is not sufficient to account for the appearance of
the largest medullated nerve fibers in each instance in the segment
nearest to the body. A peripheral factor seems to be present
here.
At the moment it is sufficient to inquire as to the information
regarding the factors determining the size of the medullated
nerve fibers which may be drawn from the present investigation.
It has been pointed out that, unlike the oculomotor nerve, the
number of medullated viscero-motor fibers is small, and that the
number of very small medullated nerve fibers is much less in the
adult than in a rat of seven days.
Among the possible influences upon the size of the medullated
nerve fibers has been mentioned the size of the animal. Dhere
('03) has shown that the extraction of myelin is greater among
mammals of greater size than among those of less size. It will
be interesting to inquire as to the influence of weight among the
individual groups of white rats. Comparing females with females
and males with males, table 1, in each group of fixed age, the
SECOND CERVICAL NERVE OF THE RAT 151
heavier individual tends to have the larger average size of the
largest nerve fibers. To this law there are a few exceptions, but
in each instance the individual of greater weight but with the
smaller nerve fibers was found to have a greater number of nerve
fibers in this spinal root.
The correlation, then, is not between body weight and size of
the nerve fibers, but between body weight on the one hand and
number and size of the nerve fibers on the other hand. Of the
two factors, the size of the fiber is more affected by the body
weight than by the number of* fibers. The larger fibers may be
found with greater body weight and greater number but when less
size of fibers is found with greater body weight the compensating
factor is the increased number of nerve fibers. This relation
appears to be an argument in the establishment of a definite
relation between the amounts of innervated and innervating material.
Size of the fibers appears to have little relation to the body
weight when the sexes are considered together. There are but
slight deviations in size of the largest medullated nerve fibers in
males and females of the same age but of widely diverse weights.
Body weight without regard to age is misleading when used for
a criterion of the size of nerve fibers. Selecting at random from
table 1 a male and a female of a weight less than 200 grams, one
might chance upon a female of 187.96 grams weight and a male
of 189.70 grams weight. The male however is seventy-four days
old, the female two hundred and seventy days of age. The male
has seven hundred and twenty-six medullated nerve fibers in the
ventral root of the second cervical nerve, the female eight hundred
and fifty-three fibers. The average area of the ten largest medullated nerve fibers in the male is 117.67 square micra and of their
axes 52.81 square micra, while for the female the average area
for the fibers is 261.87 square micra and for their axes 131.92
square micra. This may be analogous to the condition found in
the spinal cord by Donaldson ('08, p. 371). In those findings, in
rats of the same body weight without regard to age, female rats
were found to have heavier spinal cords than the males. The
152
ELIZABETH HOPKINS DUNN
amount of medullation and size of the fibers might increase the
weight of the cord.
A further step in the comparison of males and females of the
same ages but of different weights is the recognition of the fact
that among mature rats, the females, which rarely attain the
weight of the males, must have a mass or bulk of the peripheral
nervous system much greater in proportion to the body weight
350
300
250
IZ^ F
150
100
50
grams
50 100 150 200 250 300
days
Fig. 5 / is plotted to show the body growth for the female rats of eacli Kroiip
and G the curve for the male rats of the same groups. These curves are to be contrasted with those in fig. 0, which show the curves for the growth of the largest
nerve fibers.
than tliat of the males. Increased weight in the spinal cord in
the female has been interpreted as due to the richness of visceral
innervation, especially of the pelvic organs. But in this second
cervical nerve an excess over the males is found with very few or no
SECOND CERVICAL NERVE OF THE RAT
153
viscero-motor medullated nerve fibers, so that the proportional
greater pathway for impulses is furnished by the somatic motor
system. An interpretation of this condition is difficult, since there
seems to be nothing in the bodily functions of the muscles to
require or explain richer somatic innervation in the females of a
given age. In plotting the curve for the number of rats used in
this investigation there seems to be no association between the
300
250
200
150
100
50
0|a
/
^
/
Xw
/
x"
^
50
days
100
150
200
- Fig. 6 H\s, plotted to show the growth curve of the largest nerve fibers for the
female rats of edch group, and I for the male rats of each group (table 2).
early checking of body growth in the female and the growth of
the nerve fiber. The latter goes on as rapidly or more rapidly
in the female after the checking in rapidity of body growth as it
does in the male with a more prolonged growth. A comparison
of fig. 6 with fig. 5 makes this clear. Fig. 5 gives the curve for
body growth for the two males (G) and the two females {¥) of
each group. Fig. 6 gives the curves for the nerve fiber growth of
the same rats, B. for the females and I for the males.
154 ELIZABETH HOPKINS DUNN
In the interpretation of all investigations on the albino rat
much gratitude is due to Professor H. H. Donaldson now of The
Wistar Institute of Anatomy and Biology at Philadelphia, for
his preliminary studies upon the rat. Growth questions in general are of especial value to us with reference to human young.
Professor Donaldson over a long period of years, more than ten
to my knowledge, has been inspiring a series of studies of a more
and more critical nature upon the albino rat as preliminary and
comparative studies to those on the human body. An outline
of some of his plans accomplished and projected is to be found in
the President's address before the Philadelphia Neurological
Society (Donaldson, '11).
While the present investigation was undertaken independently,
it owes much for its interpretation to the solid and illuminating
researches just mentioned. It is interesting to find a laboratory
animal which in so short a lifetime as three years so conveniently
reproduces many of the conditions found in the human being,
because of this recapitulation, growth conditions in the peripheral
nervous system of the albino rat have the added value of aiding
in the interpretation of anatomical and functional conditions in
the human body.
CONCLUSIONS
During the period of rapid growth, shown in the albino rat in
the accompanying tables from the seventh to the thirty-sixth
day, there is a parallel increase of the number of medullated nerve
fibers in the ventral root of the second cervical nerve. When the
sexes are considered separately, the heavier individual at each
age has the greater number of medullated nei-ve fibers. Neither
of these relations is so definitely marked among the adult rats.
In this series of observations there is found a continuous increase in the size of both the medullated nerve fibers and their
axis cylinders to nine months of age. Among the old rats about
six hundred and forty days of age, there is a noticeable decrease
in size from that of the nine month rat both in the nerve fiber
and its axis cylinder.
SECOND CERVICAL NERVE OF THE RAT 155
The growth of the medullary sheath as compared with that of
the axis cylinder is emphasized in this series. At seven days the
area of a cross section of the axis cylinder is noticeably larger
than that of the medullary sheath. After that age the medullary
sheath grows more rapidly than the axis cylinder, at fourteen
days having a greater area than the axis cylinder. At thirty-six
days it has one and one-fourth times the area of the axis cylinder.
From thirty-six days the axis cylinder grows more rapidly until
at nine months there exists the one-to-one relation of the adult
which has been found in many vertebrates including the albino
rat. In old age there is a relatively greater loss in the axis than
in the medullary sheath, so that the area of the medullary sheath
is the greater.
While male and female rats may be grouped together in the
study of the influence of age upon the size of the medullated nerve
fibers, accuracy demands their separation when the influence of
weight is to be considered. The growth curve for the two sexes
appears to be different for the individual elements of the nervous
system, as it has been shown to be for the central nervous system
and for the body.
Usually for both males and females of a fixed age the greater
average area of the largest medullated nerve fibers of the ventral
root fibers of the second cervical nerve is found with the greatest
body weight. But if the less fiber area is found with greater
body weight the number of fibers is always greater. Greater
number may be found with greater area and greater body weight.
This correlation between the body weight and the size of the medullated nerve fibers is an argument in favor of the theory of a
certain relation between the amount of tissue to be innervated and
the caliber of the innervating pathway.
In the later periods of growth among both males and females the
size of the medullated nerve fiber runs more closely parallel with
the body weight than among the more immature individuals,
that is, growth processes in the individual nerve elements are more
rapid and also more variable among the immature than among
more mature individuals.
156 ELIZABETH HOPKINS DUNN
The comparison of mature males with mature females shows
that, while the body weight of the females may be much less than
that of the males of the same age, there is no marked difference
in the size of the largest nerve fibers, so one may say in general
that the largest nerve fibers in mature females are much larger in
proportion to the body weight than are those of mature males
of the same age, that is, the efferent pathway is greater in the
female than in the adult male of the same age.
LITERATURE CITED
Apolant, H. 1896 Ueber die Beziehungen des Nervus oculomotorius zum Ganglion ciliare. Arch. f. mikr. Anat., Bonn, Bd. 47, S. 655-668.
BouGHTON, Thomas Harris 1906 The increase in the number and size of the
meduUated fibers in the oculomotor nerve of the white rat and of the
cat at different ages. Jour. Comp. Neur., vol. 16, pp. 153-165.
Dh^r^, Charles 1903 Sur I'extension de la my^line dans le n^vraxe chez dea
sujets de differentes tallies. Comptes rendus de la Soci^t^ de biologie,
t. 55, pp. 1158-1160.
Donaldson, Henry H. 1908 A comparison of the albino rat with man in respect
to the growth of the brain and the spinal cord. Jour. Comp. Neur.,
vol. 18,, pp. 345-390.
1911 President's address. Journal of Nervous and Mental Disease,
vol. 38, pp. 257-266.
Donaldson, Henry H. and Hoke, G. W. 1905 On the areas of the axis cylinder
and medullary sheath as seen in cross sections of the spinal nerves of
the vertebrates. Jour. Comp. Neur., vol. 15, pp. 1-16.
Donaldson, H. H., Watson, J. B., and Dunn, E. H. 1906 A comparison of the
white rat with man in respect to the growth of the entire body. Boas
Memorial Volume, New York.
Dunn, Elizabeth Hopkins 1900 The number and size of the nerve fibers innervating the skin and muscles of the thigh in the frog (Rana viiescens
brachycephala, Cope). Jour. Comp. Neur., vol.10, pp. 218-242.
1902 On the number and on the relation between diameter and distribution of the nerve fibers innervating the leg of the frog (Rana virescens brachycephala. Cope). Jour. Comp. Neur., vol. 13. pp. 297-328.
SECOND CERVICAL NERVE OF THE RAT 157
1908 A study in the gain in weight for the light and heavy individuals
of a single group of albino rats. Anat. Rec, vol. 2, pp. 109-111.
1909 A statistical study of the medullated nerve fibers innervating the
legs of the leopard frog, Rana pipiens, after unilateral section of the
ventral roots. Jour. Comp. Neur., vol. 19, pp. 685-720.
Gaskell, W. H. 1886 On the structure, distribution and function of the nerves
which innervate the visceral and vascular system. Journal of Physiology, vol. 7, pp. 1-80.
Hatai, Shinkishi 1903 On the increase in the number of medullated nerve fibers
in the ventral roots of the spinal nerves of the growing white rat. Jour.
Comp. Neur., vol. 13, pp. 177-183.
1908 Preliminary note on the size and condition of the central nervous
system in albino rats experimentally stunted. Jour. Comp. Neur.,
vol. 18, pp. 151-155.
Langley, J. N. 1896 Observations on the medullated fibers of the sympathetic
system and chiefly those of the grey rami communicantes. Journal of
Physiology., vol. 20, pp. 55-76.
Ranson, S. Walter 1908 The architectural relations of the afferent elements,
entering into the formation of the spinal nerves. Jour. Comp. Neur.,
vol. 18, pp. 101-119.
Roth, A. H. 1905 The relation between the occurrence of white rami fibers and
the spinal accessory nerve. Jour. Comp. Neur., vol. 15, pp. 482^93.
TozER, Frances M. and Sherrington., C. S. 1910 Receptors and afferents of
the third, fourth and sixth cranial nerves. Proceedings of the Royal
Society of London, Series B, vol. 82, pp. 450-457.
WiLLEMS, Edguard 1911 Localisation motrice et kinesthesique. Les noyaux
masticateur et mesencephalique du trijumeau chez le lapin. Le Nevraxe, t. 12, pp. 1-220.
THE STRUCTURE OF THE SPINAL GANGLIA AND OF
THE SPINAL NERVES
S. WALTER RANSON
Northwestern University Medical School^
FIFTEEN FIGUKES
The application to the spinal ganglion of the reduced silver
method of Cajal has brought to light many new facts (Cajal, '05)
and the renewed interest in this subject has found expression in a
number of investigations including that of Dogiel ('08) . The present paper is concerned, in part, with a confirmation of these newer
observations and in part with observations which, though touched
upon by Dogiel and Cajal, escaped serious consideration by either
of them.
For this work the largest spinal ganglia (L vi, vii, S i) in large
dogs were subjected to the pyridine-silver (modified (Cajal)
technique, an account of which has already been published (Ranson, '11). Pieces of fresh nerve are placed for two days in absolute alcohol containing 1 per cent of concentrated ammonia;
washed one to three minutes in distilled water; placed in pyridine
for twenty-four hours, after which they are washed in many
changes of distilled water for twenty-four hours. They are then
placed in the dark for three days in a 2 per cent aqueous solution
of silver nitrate at 35° C; then rinsed in distilled water and placed
for one day in a 4 per cent solution of pyrogallic acid in 5 per
cent formalin. Sections are cut in paraffin and after mounting
are ready for examination. With fresh pure chemicals, absolutely clean utensils, and a reasonably constant temperature this
method can be relied upon to give uniform results.
^ The work upon which this paper is based was done in the Anatomische Anstalt,
Freiburg i. Br. My thanks are due to Professors Wiedersheim and Keibel, through
whose courtesy it was possible for me to carry on the investigation.
159
160 S. WALTER RANSON
The ganglia were cut into sections 18/x thick. It is difficult
to make use of thicker sections because the silver method, unlike
the intra- vitam use of methylene blue, brings out all the nerve
elements so that very thick sections are confusing. On the other
hand it is difficult except in thick sections to follow the axons
to their bifurcation.
Types of spinal ganglion cells according to external form
1. The simple unipolar cell. From the body of a cell of this
type arises a single axon, which after a longer or shorter, straight
or convoluted course divides dichotomously into a thin fiber
directed toward the spinal cord and a much thicker fiber running
into the nerve. These represent, according to my observations,
the great majority of the cells in the spinal ganglia of the dog.
In sections 18/^ thick it is only in a small proportion of the axons
that the entire course from cell body to bifurcation can be seen.
For the most part it is possible to follow the axons for only a limited
distance before they leave the level of the section. Many axons
can be seen dividing but these can rarely be followed back to
their cells of origin. Nevertheless this connection is so well
established that it needs no confirmation.
In the case of (a) the large cells, the axon is usually much
convoluted in the immediate vicinity of the cell and within its
connective tissue capsule, but in some cases the coil is wanting.
In other cases the axon is very short and divides almost immediately after leaving the cell. These axons acquire a myelin
sheath and stain by the pyridine silv^er method a light yellow.
(b) All of the small cells and some of the medium sized ones
present a different picture (fig. 1). The axon (whose thickness
varies with the diameter of the cell) is thin and stains a dark
brown or black. These axons seldoyi make complicated coils
about the cells, but run more or less directly toward the central
fiber bundles of the ganglia. Here these fibers can be seen in
large numbers dividing in the manner of a J' or F into a very
fine centrally directed fiber and a somewhat thicker one running
toward the nerve (fig. 2). These branches together with others
THE STRUCTURE OF THE SPINAL GANGLIA 161
of similar origin and appearance form bundles of fine black fibers
which can be followed into the dorsal root on the one side and
into the peripheral nerve on the other. These axons are devoid
of a myelin sheath (or according to Dogiel, some of them may
present a thin and interrupted coat of myelin similar to that
which is seen on some sympathetic fibers).
The axons in fig. 1 show about the average amount of coiling;
but while in many cases they are almost straight, in a few the
winding is as pronounced as that of the axon of any large cell.
It is of interest to compare the bifurcation of these fibers with
that of the meduUated axons (fig. 2). These latter branch at a
node of Ranvier and show a marked constriction both of the
main stem and the two branches at the point of bifurcation. In
none of the dividing non-medullated fibers is such a constriction
to be seen. Instead there is a broad triangular area at the point
of the bifurcation. These fibers differ then from the medullated
in their small size, in the intensity with which they stain with
silver, in the absence of a surrounding unstained ring of myelin,
and in the manner of their bifurcation.
The description which is here given of the small cells and their
axons is in no sense new. Dogiel in 1897 gave a very satisfactory
account of them, which was confirmed by Cajal ('07) and later
again by Dogiel ('08, p. 33). Dogiel found on some of these
fibers very fine myelin sheaths which disappeared and reappeared
from stretch to stretch along the fiber. It is strange that neither
author gave any further consideration to these axons, apparently
overlooking the fact that they outnumber the medullated fibers
by as much as the small cells outnumber the large. We will
return to the significance of these observations in another part
of this paper.
2. Cells whose axons have collaterals ending in end bulbs. Dogiel's type ii, Cajal's type vi. The peculiarity of these cells lies
in the fact that the axon gives off fine collaterals, which after
a course usually of no great length, end in characteristic swellings,
which according to their location may be divided into three subgroups: (a) In the majority of the cases the collaterals are given
off from the axon before it has left the connective tissue capsule
162 S. WALTER RANSON
which surrounds its cell of origin. The collateral is usually short
and directed toward the surface of th-e cell but may be long and
coiled in its course. It ends in a bulb which lies upon the surface
of the cell from the axon of which it arose (fig. 3). The terminal
swelling may be very large in proportion to the size of the collateral, and in some cases the latter increases in thickness as it
approaches the end-bulbs. These bulbs take only a light stain
with silver, appearing bright yellow. They lie upon the surface
of the cell beneath the connective tissue capsule and produce as a
rule a depression of the cell surface, (b) Sometimes the collateral
is given off from the axon at some distance from its cell of origin —
and piercing the connective tissue capsule of another cell terminates in an end bulb which lies upon the surface of this second
cell (fig. 4) . (c) Still other collaterals run in the connective tissue
of the ganglion and end there in bulbs surrounded by a special
capsule. Sometimes two or three such bulbs lie together in a
felt-work of fine fibers and the whole mass is surrounded by a
capsule.
Huber ('96) was the first to describe these structures but saw
only those that fall under subhead (a). Both Cajal and v. Lenhossek considered that some of these fibers were fine dendritic
branches arising directly from the cell body. On this point
my observations agree with those of Dogiel for in every case
where the origin could be determined they arose as collaterals
from axons and never as fine dendrites. According to Cajal and
Dogiel the axons of cells of this group, after having given off
the collaterals just described, end by dividing after the manner of
a, T or Y into central and peripheral fibers.
3. The axon of a cell of this type splits up into a number of
branches which with or without further branching are finally
reassembled into a single axon. In sections IS/x thick it is not
possible to see in their entirety such complicated structures
of this sort as were seen by Dogiel in his thicker sections and
whole mounts; but the simpler forms are often included within a
single section. A relatively common arrangement is seen in fig.
5. The axon divides into two fibers which may or may not be
of equal size and which soon reunite. A somewhat more compli
THE STRUCTURE OF THE SPINAL GANGLIA 163
cated form is shown in fig. 6. Here the axon breaks up into a
number of fibers which unite with each other to form a plexus
out of which a single axon is again formed. Sections through
much more comphcated networks formed by splitting axons can
often be seen.
4. In another variety, closely related to those just described,
the axon arises from the cell by two or more roots, each of which
has the appearance of an axon and forms a conical expansion at
the point of origin from the cell. Each of these roots may branch
repeatedly. These branches then reunite with each other forming a more or less complicated network, out of which a single axon
arises (fig. 7).
Groups 3 and 4 are closely related in that the cells of the latter
differ from those of the former only in the fact that the splitting
involves the initial portion of the axon. In both cases it is rare
to find a- myelin sheath on the fine fibers forming the plexus.
These two groups correspond to Dogiel's types v and vi taken
collectively, but the basis of separation into the two groups is
different. It is quite bewildering to read Dogiel's description of
types V and vi with their subvarieties and try to determine
what the basis of classification of his seven subvarieties into these
two major groups might have been. For this reason it has
seemed best to adopt as a basis of classification the more obvious
and apparently more fundamental difference in the origin of the
axon by a single or by a number of roots.
According to Dogiel the axons of both types, after exhibiting
their peculiar plexiform arrangements course as single axons for
some distance and finally divide in the manner of a T or Y into
central and peripheral fibers, a point which could not be verified
in the relatively thin sections with which I worked. It was, however, chiefly the origin of the axon from several roots, the splitting of the axon or its roots, and the formation of plexuses in its
course which most needed confirmation ; the final division of the
axon as described by Dogiel agrees so well with our former knowledge of the ganglion that it may safely be accepted. The cells
included in groups 3 and 4 are fully as numerous as those in
group 2; and if one might be permitted to make a very rough
THE JOORNAL OF COMPARATIVE NEUKOLOGT, VOL. 22, NO. 2
164 S. WALTER HANSON
estimate they might be said to represent together about 3 per
cent of the total number in the spinal ganglia of the dog. In the
horse, according to v. Lenhossek, they are very much more
numerous.
5. Cajal's 'fenestrated' cells are characterized by the presence
of excavations in their substance. These are most commonly
found in the neighborhood of the origin of the axon, where they
often cause a U-shaped mass of protoplasm to be raised from
the surface of the cell. The axon usually arises from the summit of such a loop. Fig. 8 shows a simple cell of this kind and
fig. 9 a more complicated one. These excavations are filled with
small cells, 'subcapsular or satellite cells.' It is only in the poorer
of the pyridine silver preparations, however, that these sateUite
cells are stained. Dogiel was unable to find the fenestrated cells
in his preparations — and concluded that Cajal had seen and
wrongly interpreted certain cells of our type iv.
Indeed it seems that among his fenestrated cells Cajal has
figured and described some which more properly belong with the
cells of the preceding variety. There is, however, a group to
which the term 'fenestrated' properly appHes, such as those seen
in figs. 8 and 9. In these the network is formed by protoplasmic
loops, while in figs. 5, 6 and 7 the axon is itself broken up to form
the network. In the fenestrated cells the axon is usually smaller
than the protoplasmic loops from which it arises, while in the
other varieties the size of the fibers forming the network is always
smaller than that of the axon and depends upon the number of
such fibers into which the axon has been split.
In addition to the cells of the varieties just enumerated, one
bipolar and two multipolar cells were seen in the sections of the
spinal ganglia of the dog. Fig. 10 represents a multipolar cell
with short, club-shaped processes, and fig. 11 a cell of Dogiel's
type XI, which, according to his more complete pictures, possesses
many medullated processes which divide repeatedly, breaking
up into fine branches with expanded ends.
According to Nageotte ('07) the fibers ending in end bulbs
resemble those seen in large numbers in transplanted ganglia and
are therefore to be regarded as being the product of regenerative
THE STRUCTURE OF THE SPINAL GANGLIA 165
activity in the neurone. Cajal ('07) accepts this interpretation
and Bielschowsk}^ ('08) extends it to the fenestrated cells and to
the cells whose axons have plexuses intercalated in their course.
On this hypothesis one would expect to see an increase in the
number of such cells after the division of the associated nerve.
With this in mind the left sciatic nerve was cut in four dogs and
after one month the associated spinal ganglia were prepared by
the pyridine silver technique. The results of these experiments
were entirely negative. There was no increase in the number of
fine fibers ending in end bulbs nor were any other of the peculiar
cell types seen in the normal ganglia increased in number.
Since the division of the axons might be expected to be as efficient
as any stimulus in producing regenerative changes in the neurone,
these experiments, so far as they go, speak against the interpretation of these new cell types as the expression of a slow regeneration constantly going on in the normal ganglia. Other
experiments are in progress with the purpose of making a more
complete test of the hypothesis of Nageotte.
The axons of the small cells
In concluding his section on the cerebro-spinal ganglia in
'Plasma und Zelle,' Heidenhain ('11) says:
Es wiirde gewiss fiir die Physiologie von grosser Bedeutung sein
wenn wir behaupten konnten, das wir mit der Anatomie der cerebrospinalen Ganglion im reinen sind. Dies ist jedoch nicht der Fall. Erstlich
ist der Ursprung der erwahnten afferenten sympathischen Fasern leider
nicht naher bekannt .... Und zweitens befindet sich nach
den Zahlungen von Gaule und Lewin, ebenso von Biihler in den Ganglien eine ausserordentliche Ueberzahl von Zellen deren P'ortsatze wir
noch nicht kennen.
It is with this second problem that we wish now to deal. The
numerical excess of spinal ganglion cells over medullated afferent
fibers is well established as table 1 shows, although in most cases
it is not so great as that found by Gaule and Lewin in the 32d
spinal nerve of the rabbit.
Hatai ('02) by a separate enumeration of the large and small
cells of the (iv C, iv T and ii L) sphial ganglia of the white rat,
166 S. WALTER RANSON
TABLE I
Ratio of spinal ganglion cells to dorsal root fibers
NUMBER OF
GANGLION
CELLS
NUMBER OF
MEDULLATED
AFFERENT
NERVE FIBERS
Gaule and Lcwin ('9G) ..:... I Rabbit , i Coc. 20,361 3,173
Hatai ('02) ' White rat vi C 12,200 4,227
Hatai ('02) , White rat | ii L 9,442 | 1,644
Raiison ("08) \ White rat ' ii C 7,721 2,472
showed that the small cells constitute about 60 per cent of the
total number, while Warrington and Griffith ('04) working with
the II C. spinal ganghon of the cat estimated the small cells as
constituting 70 per cent of the total number. Now we have
shown in a former paragraph that the axons of these small cells
are non-medullated and it is therefore clear that they could not
be taken into consideration in the enumeration of the afferent
fibers represented in table 1 based as it was in every case upon a
differential myelin sheath stain. It is to these non-medullated
fibers, the axons of the small spinal ganglion cells, that we are to
look for the explanation of the discrepancy between the number
of spinal ganglion cells and medullated afferent fibers. If a count
of the afferent axons were made, the number would probably
closely approximate that of the spinal ganglion cells.
We have shown in fig. 1 how these non-medullated fibers arise
from the small cells, in fig. 2 how they divide dichotomously
into a thin fiber directed toward the dorsal root and a slightly
thicker one directed toward the nerve. These branches unite
themselves into bundles of fine black fibers which course longitudinally through thp ganglion — along with the medullated fibers
having an analogous origin from the large cells. These bundles
of non-medullated fibers can be followed into the dorsal root to
which they give an appearance wholly different from that of the
ventral root. Similar bundles of non-medullated fibers can be
followed into the nerve. Fig. 12 shows the point of union of the
ventral and dorsal roots to form the mixed nerve. It can be seen
at a glance that the composition of the dorsal root (a), as it streams
out of the spinal ganglion to unite with the ventral root (6) differs
THE STRIH'TUHE OF THE SPINAL riAN(iMA 167
markedly from tlio lattor because of the ])un(lles of i'liw black fibers
which it contains. Ouo can see this contrast in a sti-ikiii^- way
where the bundles from the two roots decussate as (ibci-s from the
ventral root run into the dorsal ramus (d) and others from the
dorsal root into the ventral ramus (r). Fiji;. 13 repn^sents a portion of this decussation under hiji;li(M' maf^uificatioii. in the
center is a pvu'e l)un(ll(' of incduil.-iled fibci's derived fi'oiii the
ventral root, while tlie fibers taking' the other dii'cction nre dei'ived
from tlie dorsal root, and of these some are medullated but more
are non-medullated.
It has not been possible to show that no non-medullated fibers
run into the nerve from tlu^ ventral root, but if present they are
in very small number. The majority of such fibers seen in the
nerve can be directly traced into the spinal ^anj^lion. Nor has
the contribution of the ramus commtmicans to tlie non-niedidlated fibers of the nerve been investi^at(;d, but even this must be
small compared to the enormous numbers coming through the
dorsal root.
As to what ultimately becomes of these fibers, thc^re are as yet
no observations. That the central branches of the non-medullated axons enter the spinal cord, there can be no doubt, but their
distribution within it has not yet been investigated. That their
perii)heral branches run for long distances in the n(>rve has been
shown in a previous paper. They have been demonsti-at-cd in
the sciatic nerve of man, dogs, cats, rabbits and rats (Hanson,
'11). Figs. 14 and 15 have been drawn with the aid of a camera
lucida from adjacent sections of tlu^ same human sciatic luu've,
the one (fig. 14) prepared according to the ]^d-Weig(M-t- t('clini(|ue
and the other ffig. 15) by the Cajal silv(!r method. The magnification is the same in both instances. (Jreat care was exei-cised
not to decolorize any medullated fibers in differentiating the PalWeigert preparations and the field from which fig. 14 was drawn
was chosen because it exhibited the maxinumi number of small
medullated fibers. In the Cajal i)reparation (fig. 15) the colorless rings represent the myelin sheaths, within wiiicii nrc liglitly
stained axons. In the interspaces between these medullated fibers
are enormous numbers of small black axons directly imbedded
168 S. WALTER RANSON
in the connective tissue from which they are only separated by a
thin neurilemma. The number of axons medullated and nonmedullated which can be seen in the Cajal preparation far exceeds
the number of myelin sheaths demonstrated by the Pal-Weigert
method.
In summing up this point it may be said that the small cells
of the spinal ganglion exceed in number the large cells, that their
axons are non-medullated and divide after the manner of a T
or Y into a central and a peripheral fiber. The former runs into
the spinal cord and the latter can be followed for long distances
in the spinal nerves, but the ultimate distribution of neither the
centrally nor peripherally directed branch has yet been determined.
BIBLIOGRAPHY
BiELscHowsKY, AI. 1908 tJber den Bau der Spinalganglien unter iiormalen
und pathologischen Verhaltnissen. J. f. Psychol, u. Neurol., Leipz.,
Bd. 11, pp. 18S-227.
Cajal, S. R. 1905-06 Trab. del Laborat. de Investig. Biol., vol. 4. Ref. Rev.
Neurol, and Psych., vol. 4, p. 124.
1907 Die Structur der sensiblen Ganglien des Menschen und der Tiere.
Anat. Hefte, Zweite Abt., Bd. 16, p. 177.
DoGiEL, A. S. 1897 Zur Frage iiber den feineren Bau der Spinalganglien.
Internat. Monatsschr. fiir Anat. u. Physiol., Bd. 14, p. 73.
1908 Der Bau der Spinalganglien des Menschen und der Saugetierc.
Jena.
Gaule and Lewin 1896 tJber die zahlen der Nervenfasern u. (!angli(>nzollen
des Kaninchens. Centralbl. f. Physiol., H. l,"") u. 16.
Hatai, Shinkishi 1902 Number and size of the spinal ganglion cells and dorsal root fibers in the white rat at different ages. Jour. Comp. Neur.,
vol. 12, p. 107.
Hkidenuain, M. 1911 riasina und Zelle. Jena, 1911.
HuBEK, G. Caul 1896 The spinal ganglia of Amphil)ia. Aiia(. Auz., Hd. 12,
p. 4J7.
LioxnossfiK, Al. v. 1907 Zur Ktmntnis der S|)inalgang!ienzellen. .\rch. f.
Mikrosk. Ai:at., Bd. 69.
THE STRUCTURE OF THE SPINAL GANGLIA 169
Levi, G. 1905 Beitriige zur Kenntnis der Structur dcs Spinalgangliens. Anat.
Anz., Bd. 27.
Marinesco, G. 1906-07 Quelques recherches sur la morphologie normale et
pathologique des cellules des ganglions spinaux et sympathiques de
I'homme. N^vraxe, Louvain, vol. 8, pp. 7—38.
Nageotte, J. 1907 a Deuxieme note sur la greffe des ganglions rachidiens'
Comp. Rend. Soc. Biol., Paris, vol. 62, p. 289.
1907 b Recherches experimentales sur la morphologie des cellules et
des fibres des ganglions rachidiens. Rev. Neurol., Paris, vol. 15, p. 357.
Ranson, S. W. 1908 The architectural relations of the afferent elements entering into the formation of the spinal nerves. Journ. Comp. Neur., vol.
18, p. 101.
1911 Non-medullated nerve fibers in the spinal nerves. Am. Jour.
Anat., vol. 12, p. 67.
Warrington, W. B., and Griffith, F. 1904 On the cells of the spinal ganglia
and on the relationship of their histological structure to the axonal
distribution. Brain, vol. 28, p. 297.
PLATE 1
EXPLANATION OF FIGURES
The drawings are, with the exception of figs. 14 and 15, free hand sketches from
pyridine silver preparations of the spinal ganglia of dogs. Figs. 14 and 15 are
camera lucida tracings from a human sciatic nerve, the section from which fig.
14 was drawn having been prepared by the Pal-Weigert method, and that from
which fig. 15 was drawn by the Cajal method.
1 Small and medium sized cells with non-medullated axons. Non-medullated fibers black, medullated fibers gray.
2 Bifurcation of a medullated fiber and four non-meduUated fibers. The
latter are fine and black with a triangular expansion at the point of bifurcation,
the former is large and grey (in the preparation light yellow) with a constriction
at the point of bifurcation.
3-4 Collaterals ending in end bulbs.
5-6 Cells whose axons are split to form a plexus.
7 A cell whose axon arises by three roots which form a plexus out of which
the axon is formed
8-9 'Fenestrated' cells.
10 Multipolar cell.
11 Cell of Dogiel's type xi.
170
THE STRUCTURE OF THE SPINAL GANGLIA
S. WALTEU KANSON
PLATE 1
171
PLATE 2
EXPLANATION OF FIGURES
12 Nerve just distal to spinal ganglion; a, dorsal root just outside the
ganglion; b, ventral root; c, ventral ramus of nerve; d, dorsal ramus of nerve; e,
an arrow points to a central bundle of ventral root fibers running into the dorsal
ramus.
13 Higher magnification of the central portion of fig. 12. The central
bundle is derived from the ventral root and contains only medullated fibers; the
fibers passing in the otlier direction are from the dorsal root. A large part of these
are non-medullated.
172
THE STRUCTURE OF THE .SPINAL GANGLIA
S. WALTER HANSON
PLATE 2
"^^^.
^>s^
12
173
PLATE 3
EXPLANATION OF FIGURES
14 Human sciatic nerve in cross section. Myelin sheaths as black rings.
15 From same nerve as fig. 14, axons black, myelin sheaths colorless.
Non-medullated fibers in the interspaces between the medullated ones.
174
THE STRUCTURE OF THE SPJNAL GANGLIA
S. WALTER HANSON
PLATE 3
'«o
15
175
THE OLFACTORY TRACTS AND CENTERS IN
TELEOSTS
RALPH EDWARD SHELDON
Assistant Professor of Anatomy, the University of Pittsburgh Medical School
From the Hull Laboratory of Anatomy of the University of Chicago
ONE HUNDRED AND FORTY-TWO FIGURES
CONTENTS
I. Introduction 178
II. Anatomy 182
1. Peripheral olfactory apparatus 183
a. Olfactory capsules 183
b. The olfactory nerve 185
c. The ganglion of the nervus terminalis 186
2. The telencephalon 186
a. The olfactory bulb and crus 186
b. The cerebral hemispheres 189
(1) Gross morphology 189
(2) Nuclei 191
3. The diencephalon •. 198
a. Rostral limits 198
b. Gross morphology 199
(1) Epithalamus ; ! . 201
(2) Thalamus : 201
(3) Hypothalamus 204
4. The fiber tracts 207
a. Crural tracts 207
(1) Tractus olfactorius lateralis 209
(2) Tractus olfactorius medialis 210
(3) Nervus terminalis 212
(4) Distribution secondary olfactory fibers in forebrain... 212
b. The anterior commissure 213
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3
JUNE, 1912
178 RALPH EDWARD SHELDON
c. Diencephalic connections 214
(1) Tractus olfacto-habenularis 214
(2) Fasciculus retroflexus 217
(3) Tractus habenulo-diencephalicus 217
(4) Posthabenular preoptic connections 218
(5) Epiphyseal fibers 218
(6) Fasciculus medialis hemisphaerii 219
(7) Fasciculus lateralis hemisphaerii 222
(8) The nucleus preoptions and its connections 227
5. The conduction pathways 231
6. The morphological areas of the forebrain 238
III. Discussion 239
IV. Literature cited 248
V. Figures 254
I. INTRODUCTION
The information here added to that heretofore existing in the
Hterature is derived largely from a study of the olfactory apparatus
in the carp, Cyprinus carpio (L). The olfactory apparatus is
highly developed in the cyprinoids which, therefore, lend themselves readily to its study. For the elucidation of difficult points,
however, comparison has been made with Weigert and Golgi
sections of the brains of the pike, Lucius lucius (L), the goldfish, Carassius auratus (L) and the catfish, Ameiurus nebulosus
(Le Sueur).
I am indebted to Prof. C. Judson Herrick for helpful suggestions and criticism in every phase of the work, together with the
opportunity to use his unexcelled neurological library and his
personal material. Prof. R. R. Bensley likewise placed at my
disposal all the facilities of the department, including the services
of the artist, Miss Katharine Hill, who has drawn, with the most
painstaking care, the larger portion of the figures. Through the
kindness of Prof. Charles Brookover, of Buchtel College I have
been able to examine preparations of the brain of Amia calva and
to secure well preserved material for most of the Ram6n y Cajal
impregnations. Acknowledgments should also be made to Prof.
B. G. Wilder of Cornell University, at whose suggestion this research was undertaken, and to Prof. S. H. Gage of Cornell University and Prof. E. L. Mark of Harvard University, in whose
laboratories important parts of this investigation were conducted.
OLFACTORY CENTERS IN TELEOSTS 179
MATERIAL AND METHODS
The material used consists of the following eighty-three series
of sections of the carp brain.
/. Weigert method
Inasmuch as the method used varies somewhat from that usually followed, and since it is very successful, it will be briefly outlined here. The fish are killed in a mixture of ether and water, the
brain removed immediately and placed in 4 per cent formaldehyde for at least forty-eight hours. It is then washed in running
water for a few hours and placed in Miiller's fluid at a temperature of 40° C. for from eight to fourteen days. The fluid is
changed every second day during this period. The brain is next
washed, dehydrated, cleared in carbol-xylene and embedded in
paraffine. After the removal of the parafiine from the mounted
sections the slides are placed for twelve hours in a half-saturated
solution of copper acetate, stained three to four hours in Weigert 's hematoxylin, and differentiated in 2| per cent potassium
ferricyanide with the addition of 2 per cent borax. Pal's
modification was tried but rejected, as it was found that sections
on the slide could not be evenly differentiated; moreover, the
method outlined gives rather better results for the work in question, as it brings out the unmedullated tracts and the cell groups,"
which the Pal modification does not. There were stained according to this method:
Two series transverse sections of the entire brain.
Two series sagittal sections.
Two series frontal sections.
Six series through the olfactory bulbs and crura.
All of these were from carp 35 to 60 cm. in length and were cut
at 15 micra. In addition there were prepared one transverse
and one frontal series through the entire head of carp of 3 cm.
in length. The method followed in this case is as follows; the
fish are placed in Miiller's fluid, changed every second day, for a
month, and then decalcified for another month in Flemming's
180 RALPH EDWARD SHELDON
stronger fluid, changed each week. From this point on the
method is similar to the one first outUned; viz., dehydration, clearing, embedding in paraffine, etc. Medullated fibers and nerves
stand out very distinctly after the use of this method. Other
methods of decalcification were tried but, as Herrick ( '97) points
out, the Weigert method will not 'take' after any of the ordinary
processes of decalcification. Professor Herrick was kind enough
to loan me, in addition, a series of transverse sections through the
adult carp brain, stained by the Weigert-Pal method.
II. Chloral hematoxylin and eosin method
Entire carp, 1 cm. in length, decalcified.
Two series transverse sections.
Three series sagittal sections.
Two series frontal sections.
III. Toluidin blue method
The only fixing agent which gave uniformly good results with
this stain was Graf's chrom-oxalic for twelve hours. This method
was used for the differentiation of areas and the cytological structure of the nerve cells.
One series transverse sections.'
One series sagittal sections.
One series frontal sections.
IV . vom Rath method
This was used for the unmedullated tracts, particularly in the
olfactory bulbs, where two series of transverse sections were made.
The method followed is that given by vom Rath ('95). This
consists of fixation in the following solution for three days; saturated aqueous solution of picric acid, 200 cc, 10 per cent platinic
chloride, 10 cc, 2 per cent osmic acid, 25 cc; glacial acetic acid,
2 cc. Next the specimens are placed in methyl alcohol for 15
minutes, 0.5 per cent aqueous solution of pyrogallic acid for two
days, dehydrated for two weeks in the dark, cleared in carbol
OLFACTORY CENTERS IN TELEOSTS 181
xylene, embedded in paraffine and sectioned at 5 micra. This
method is of particular value in tracing the course of the nervus
terminalis.
V. Gold chloride method
This was used to bring out the unmedullated fibers, particularly in the olfactory bulbs; it is not of great value, however, owing
to its low penetrating power. The method of fixation in formalin
as given in Hardesty's 'Neurological technique,' was followed with
the best results. Two series of sections of the bulbs were prepared by this method.
VI. Golgi method
Individuals two to five centimeters in length.
Five series transverse sections.
One series frontal sections.
Individuals twenty-five to forty centimeters in length.
Six series transverse sections.
One series sagittal sections.
Nine series cut in various oblique planes.
Fourteen series of the olfactory bulbs cut in various
planes.
Two different methods were followed, both of which gave good
results. With most of the Golgi material the fish were killed, the
brains removed and placed for three to five days in a mixture of
two parts of 3 per cent aqueous solution of potassium dichromate
and one part of 1 per cent aqueous solution of osmic acid. Next
they were rinsed in a f per cent solution of silver nitrate in which
they may remain indefinitely but are ready for dehydration and
embedding in celloidin after two to four days. The second method
was used for brains fixed in 4 per cent formaldehyde.
After fixation for forty-eight hours the brains were washed in
running water for twenty-four hours and then placed in a 3 per
cent aqueous solution of potassium dichromate at a temperature
of 40° C. for six to ten days. They were next placed in the
osmium-dichromate mixture and treated as outlined for the first
182 RALPH EDWARD SHELDON
method. In addition to the series noted above, Professor Herrick
very kindly loaned me ten series of the brains of young carp cut
in various oblique planes. The Golgi method was used chiefly
for the study of the different neurones and the course, with particular reference to the direction, of the fiber tracts.
VII. Ramon y Cajal method
Two series transverse sections.
Three series frontal sections.
Five series sagittal sections, two of these partlj^
oblique.
Some difficulty was experienced in getting good preparations,
the following method giving the best results. Whole brains are
fixed in 95 per cent ethyl alcohol, washed for two hours in running
water, placed in a 1 per cent aqueous solution of silver nitrate
at a temperature of 35° C. for three to five days, washed in distilled water, transferred to a 1 per cent aqueous solution of hydroquinonefor twenty-four hours, washed in running water for twentyfour hours, dehydrated, cleared in cedar oil, mounted in paraffine
and cut at ten to fifteen micra. Fixation in neutral or acid formalin gave poor results.
II. ANATOMY
The names applied to the different fiber tracts and cell areas
have, so far as is consistent with their morphology, been taken
from the literature. In a few cases such terms have been used
in a sense slightl}^ different from that assigned them by the original authors; whenever such is the case the fact has been noted.
In several cases inappropriate terms of long use have been
retained owing to their familiarity and common use. Where,
however, a term is lacking in the literature, or where a previously used term is greatly at variance with the morphology, a
new name has been selected. In this case the endeavor has been,
as far as possible, to make such new name descriptive of the relationships involved, or else suggestive of a homologous structure
OLFACTORY CENTERS IN TELEOSTS 183
in the nervous anatomy of higher forms. In the case of fiber
tracts the customary methods of neurological nomenclature have
been followed, viz., the application of a term which will include in
itself full information as to the origin and termination of the
fibers as well as their direction; as for example, the tractus intermedio-habenularis, originating in the nucleus intermedius and
terminating in the habenula.
1. PERIPHERAL OLFACTORY APPARATUS
a. The olfactory capsules
The olfactory apparatus in the carp consists of the olfactory
capsules with their lamellae, open to the exterior through two
apertures; the olfactory nerves, bulbs, crura, centers in the cerebral hemispheres, epithalamus, medithalamus and hypothalamus,
to which may be added the motor connections common to the
olfactory and gustatory senses, etc. These latter will not be
considered in this article.
Gross morphology. The two external apertures of the capsules
are in close proximity, one rostro-medial of the other. They are
separated by a grooved flap of skin so shaped that in forward
movement water will be driven into the more rostral aperture.
The lateral aperture opens caudally for the exit of water from the
cup. Inside the capsule, and running caudo-laterally from the
rostro-medial aperture, is a median ridge from which the lamellae
radiate on either side and at its caudo-lateral end.
Microscopic anatomy. The lamellae are covered by the epithelium of the olfactory mucous membrane, consisting of the
typical nervous olfactory cells, and the supporting cells. Goblet
cells are particularly numerous in the epithelium of the central
ridge, which is also slightly thicker than that of the lamellae
(fig. 5). It resembles closely the respiratory epithelium of the
Schneiderian membrane of mammals, as distinguished from the
olfactory portion. It is probable, therefore, that there are found
here two varieties of epithelium, similar to the condition in higher
forms; an olfactory, concerned with smell and a respiratory,
concerned, in this case, with the water current.
184 RALPH EDWARD SHELDON
Innervation. From the olfactory cells arises the unmedullated
fibers which, passing through the lamellae, form the olfactory
nerve. Medullated fibers penetrate the central ridge, ending
immediately underneath the epithelium (fig. 5). Such an innervation has been described in no other anamniote (Sheldon,
'08 b), although it has long been known that in mammals, particularly in man, such fibers take part in the innervation of the
nasal mucous membrane.
In 1903 Rubaschkin demonstrated their presence in birds.
Practically all Amphibia and many fishes have been studied with
reference to this point, but in no case have medullated fibers been
demonstrated beyond doubt, although Aichel in 1895 believed that
he found something of the kind in embryo teleosts. In six Weigert series through the olfactory capsules, bulbs and crura of the
adult carp it has been possible to demonstrate the presence of
medullated fibers in the tunica propria of the Schneiderian membrane, part of which evidently distribute to the epithelium, as
they can be traced to the membrana propria itself. These latter
probably end in free nerve terminations, as there are no special
organs developed. Part of the fibers entering the tunica propria join the bundles of unmedullated fibers and apparently run
to the mucous membrane of the lamellae with them. The remainder of the medullated fibers innervate the skin about the
nasal capsule.
All of these medullated fibers are derived from the supraorbital trunk, which is made up of general cutaneous fibers from
the Gasserian ganglion (nervus ophthalmicus superficialis trigemini) and sensory fibers from the facial (nervus ophthalmicus
superficiahs facialis). This latter nerve is composed partly of
fibers from the dorsal lateralis ganglion, and partly of visceral
sensory fibers from the geniculate ganglion. The fibers entering
the tunica propria are certainly not acustico-lateral, since no canal
or pit organs are developed in connection with the epithelium';
the fibers are also smaller than are the lateralis fibers. They
may, therefore, be either general cutaneous or visceral sensory,
with the preponderance of evidence in favor of the former. This is
due, in part, to the fact that in birds and mammals such innerva
OLFACTORY CENTERS IN TELEOSTS 185
tion is trigeminal and partly because the weight of evidence in the
teleosts is against the supposition that visceral sensory fibers
are present in this region. Part of the branch entering the tunica
propria goes to the skin, as already noted; the number of general
cutaneous fibers in the supra-orbital trunk is much greater than
the number of visceral sensory. If there are visceral sensory
fibers going to the mucous membrane, they must be unspecialized,
as there are no taste buds present; there is not the slightest evidence, however, that such fibers are here present. In their course
from the supra-orbital trunk to the tunica propria themedullated
fibers pass partly between the two bundles of the olfactory nerve
and partly directly laterad into the median ridge.
Young gold fish and cod were studied with reference to the
presence of medullated fibers in the mucous membrane, but none
could be demonstrated. This may have been due, particularly, in
the case of the gold fish, to the fact that the individuals were
immature, as such fibers could not be found in young carp.
As the main current of water would be forced along the ridge
thus innervated by general cutaneous fibers, it is probable that
their function is that of tactile response for solid substances in the
water or else with respect to the strength of the water current
or both (see also Kappers, with respect to the 'Oralsinn,' and
Sheldon, '09 b, on 'Chemical Sense').
b. The olfactory nerve
The olfactorj^ fibers gather from the different lamellae in two
main bundles. In general, the medial bundle is derived from
the more rostral lamellae, while the lateral is derived from the
more caudal. The fibers of the two bundles distribute to all
parts of the rostral and lateral surfaces of each bulb, the lateral
bundle causing a protuberance on the dorso-lateral surface of each
bulb as shown in figs. 1, 6 (a). There is a quite general crossing
of the fibers of the two bundles before they reach the bulb so that
fibers from each reach all parts of the bulb (fig. 123). Apparently,
however, the lateral bundle is more especially associated with the
tractus olfactorius lateralis and to a somewhat less extent with the
186 RALPH EDWARD SHELDON
tractus olfactorius ascendens, while the medial bundle is most
closely associated with the tractus olfactorius medialis. The
olfactory bulb is closely applied to the caudo-mesal face of the capsule so that the nerve itself is very short, although individual
fibers may be of some length.
c. Ganglion of the nervus terminalis
Lying between the two bundles of the olfactory nerve from the
lamellae to the bulb are a number of large scattered ganglion cells
forming the ganglion of the nervus terminalis. In the adult carp
these cells are most numerous near the bulb and are apparently
about a hundred in number. This is less than is the case in Amia
as described by Brookover ('08, '10). Neurites from these cells
run mesad to form a bundle of fibers on the mesal aspect of each
bulb (figs. 7, 123, 124).
2. THE TELENCEPHALON
a. Olfactory bulb and cms
The olfactory bulb is elhpsoid in shape, about 1.5 mm. long and
1 nmi. thick, in a 40 cm. carp. Rostrally and laterally it is covered by a mass of olfactory nerve fibers as noted above. At the
rostral end of the bulb a circular constriction appears externally,
separating the bulb proper from the olfactory nerve proper, which
rostro-lateral to the constriction spreads out over the olfactory
capsule. Caudally the bulb tapers down to the small, elongated
crus on which it is borne in the cyprinoids. This is from three to
four centimeters long in a 40 cm. carp, extending from the bulbs to
the cerebral hemisphere (fig. 1). In young fry the bulbs are closely
apposed to the hemispheres; but since the cranium grows faster
than the brain as a whole, the crura elongate. Each crus is a
hollow tube, the base of which is formed by the tracts connecting
the bulb and hemisphere (figs. 2, 22, 23). Dorsally is an epithelial roof, a rhinotela, which is simply a rostral prolongation of
the tela, or so-called pallium of the hemispheres, consisting of a
layer of ependyma and one of pia. This covering arches over the
OLFACTORY CENTERS IN TELEOSTS 187
solid base of the crus at its caudal end as shown in fig. 23, gradually decreasing in extent rostrad (fig. 22) until it forms only a
roof for the trough-like cavity below. This cavity is morphologically a part of the ventricle of the hemispheres, extending, even
a short distance into each bulb, as is the case with most vertebrates (Wiedersheim, '02).
Internal to the layer of olfactory nerve fibers occurs the formatio bulbaris, formed chiefly by the glomeruli. The glomeruli
are of the usual type, consisting of the terminal end-brush of
olfactory nerve fibers, mingled with the dendrites of mitral cells,
chiefly. The central and mesal portion of the bulb is made up of
a mass of cells, the nucleus olfactorius anterior, the lobus olfactorius anterior of Goldstein.
According to Golgi preparations, neurones of several different types are found in the olfactory bulb. The most conspicuous are the large cells with short, thick, many branched dendrites,
the mitral cells (figs. 8 to 12). These are irregular in form and
are situated largely in the peripheral portion of the bulb, with
their long axes approximately parallel with the surface as figured
by Johnston, Catois, etc. The mitral cells are very irregular in
form; pyramidal, stellate and goblet shapes being the most numerous. The dendrites of these cells, as already mentioned, break
up in the glomeruli and there come into relation with the terminals
of the olfactory nerve fibers. Their neurites form the majority
of the centripetal fibers of the tractus olfactorius lateralis and
tractus olfactorius medialis. A dendrite of a mitral cell will
often enter, also, into relation with one of the cells of the nucleus
olfactorius anterior, usually a fusiform or stellate cell. The
smaller cells of the bulb are more nearly central in position and
make up most of the nucleus olfactorius anterior. Fusiform and
stellate cells are the most numerous of these, with occasionally a
pyramidal or goblet-shaped cell (figs. 13 to 20). The stellate
cells, particularly of the types shown in figs. 14 and 17, are the
most common, and are situated near the center of the bulb, with
their many processes extending fan shaped toward the periphery,
where many of them enter glomeruli (Johnston, '98, fig. 1).
Other processes of these cells enter into relation with other cells
18S RALPH EDWARD SHELDON
of the nucleus olfactorius anterior. It is certain that a few of the
stellate cells send their neurites into the hemispheres, but such
could not be demonstrated with certainty for all. Many fusiform cells of the type shown in fig. 13 lie near the center of the
bulb with two processes extending to either margin. These cells
likewise send their neurites to the hemispheres (fig. 21). Cells
of the types shown in figs. 15, 16, 18, 20 may be found in any part
of the nucleus olfactorius anterior, with their processes extending
nearly equally in all directions. Small granule cells, of the type
shown in fig. 19, are common in the center of the bulb, where they
apparently function as association cells, as no neurites entering
the crura could be demonstrated. The mitral cells undoubtedly
correspond with the mitral cells of all other vetebrates, so far
as studied; there is some question, however, regarding the comparative morphology of the smaller cells throughout the vertebrate series. Appa^-ently, as is shown also by Johnston, the stellate cells in lower vertebrates are connected with the glomeruli
and hemispheres, much as are the mitral cells; as an ascent is made
in phylogeny, however, these cells may either disappear or may
metamorphose into mitral cells. The typical stellate cells of the
carp as shown in figs. 14, 17, are undoubtedly similar to the stellate cells of the granular zone of Acipenser, as described by Johnston; there is the same relation to the glomeruli, the position in
the bulb is the same, and the central processes take the same
course. Fusiform cells of the type shown in fig. 13 are probably
the homologues of Johnston's spindle cells of the granular zone,
although no neurites were traced from these cells into the crura.
The type found in figs. 15 and 20 probably corresponds to Johnston's cells with short neurites, Golgi type II cells. Cells of Cajal
were not identified with certainty. The granule cells of the carp
are apparently simply intrinsic association nerve cells, differing,
therefore, from the granule cells of Acipenser.
The fiber tracts of the olfactory bulb will be taken up later, in
connection with the fiber systems of the cerebral hemispheres.
OLFACTORY CENTERS IN TELEOSTS 189
b. The cerebral hemispheres
(1) Gross morphology. The cerebral hemispheres are of the typical teleostean type (figs. 1 to 4). They consist of paired solid basal
lobes which contain chiefly the secondary olfactory centers, continuing caudo-ventrally over the optic chiasma as the peduncuH
thalami, or praethalamus of C. L. Herrick. Dorsally and laterally, these are covered by a membranous roof, the so-called pallium, composed of adjacent layers of ependyma and pia. This
tela is continuous rostrally with the membranous roof of each
olfactory crus, the separation into two parts occurring just at
the rostral margin of the basal lobes. This tela is attached at the
ventro-lateral margin of each hemisphere, at which point its pia
becomes continuous with that of the base of the brain, while its
ependyma is reflected over the basal lobes (figs. 1, 2, 3, 4, 34).
Immediately mesal to the attachment of the tela occurs a fissure, the fissura endorhinaUs (figs. 4, 24, 25, etc.). This is the
sinus rhinalis of Kappers ('06), the fovea endorhinalis externa of
Kappers and Theunissen ('08), the fovea limbica of Goldstein
and Edinger, the fissura ectorhinalis of Owen ('68), the fissura
endorhinalis of many authors. This fissure holds a constant position throughout the vertebrate series, separating in the higher
forms the basal olfactory centers from the pyriform lobe; it likewise bears a constant relation to the tractus olfactorius lateralis,
as will be noted later.
The ventricle of the f orebrain consists of the open space between
the tela and the basal lobes. This forms a large, but shallow
cavity, excepting between the two basal lobes where it is of some
depth (figs. 24, 34, 35, etc.). It extends caudally to the velum
transversum. Caudal to this velum, occurs a much convoluted
epithelial sac extending rostrally over the tela proper; this is
the dorsal sac, and is an evagination of the membranous wall of
the diencephalon (fig. 68) . Ventral to the velum transversum, the
forebrain ventricle passes over into the third ventricle or diencephalic cavity.
Each basal lobe is separated by ependymal sulci on the dorsal,
lateral and mesal surfaces into regions with characteristic internal
190 RALPH EDWARD SHELDON
structure and fiber connections (figs. 2 and 3). The deepest of
these is the sulcus ypsihformis, which arises from the ventrolateral border about three-fourths of the distance bsick from
the rostral pole of the basal lobe, ascends to the dorsal surface and
here divides into an anterior and a posterior limb, which enclose
a central eminence. This eminence contains the palaeostriatum
and the primordium hippocampi, the latter covering the dorsal
surface of the palaeostriatum, especially on its mesal border.
The posterior limb separates the posterior pole from the.rest of the
hemisphere ; the anterior limb separates the central eminence from
the tuberculum anterius and the tuberculum laterale, these comprising a part of the nucleus olfactorius lateralis. The remainder
of the lateral olfactory nucleus is the nucleus pyriformis of the
posterior pole.
The anterior limb of the sulcus ypsiliformis corresponds fairly
closely with the sulcus palaeopallio-epistriaticus of Thynnus and
the fovea endorhinalis interna of Amia, as described by Kappers
and Theunissen ('08).
On the mesal aspect of each basal lobe, extending for almost the
whole length of the lobe is a well defined sulcus of great morphological importance which has been ignored by other writers on
the brains of fishes. It forms the dorsal boundary of the precommissural body and has some points of resemblance with the fissura limitans hippocampi (C. Judson Herrick, '10) in Amphibia
and Reptilia, the fovea septocorticalis (Kappers and Theunissen) in Rana, and the fissura arcuata of Gaupp, with which, however, it is not fully homologous, as will appear beyond. It will
be designated sulcus limitans telencephali.
Ventrally of this furrow lies the corpus precommissurale, termed
the epistriatum by Kappers ('06), the lobus olfactorius posterior,
pars medialis, by Goldstein, etc.
An examination of fig. 4 shows that the fissura endorhinalis
on the ventral surface of the hemispheres forms an open V. It
first appears rostrally at the point where the olfactory tract joins
the hemispheres (fig. 24), gradually extending laterally until the
base of the sulcus ypsiliformis is reached, whence it turns medially
again. For the whole of its extent the tractus olfactorius lateralis
OLB'ACTORY CENTERS IN TELEOSTS 191
lies immediately dorsal, giving off fibers to the nucleus olfactorius lateralis and nucleus pyriformis. Lateral to the caudal end
of the fis'sura endorhinalis lies the nucleus teniae of Edinger,
Kappers and Goldstein.
(2) Nuclei. The basal lobes are entirely separate, excepting
ventrally, where the}^ are joined by the lamina terminalis, which
runs rostrally from the region of the optic chiasma. At a point
approximately two-thirds distant from the rostral margin of the
hemispheres, there lies embedded in the lamina terminalis, the large
anterior commissure, connecting both lobes (figs. 34 to 01).
Rostrally, the lobes overhang the olfactory tracts for a short distance (fig. 24), while caudally the hemispheres, spreading laterally over the optic tracts, are partly covered by the optic lobes
(fig. 76).
The basal lobes contain, in teleosts, the secondary olfactory
centers, one or more tertiary centers and the so-called corpus
striatum, here designated the palaeostriatum. In the carp this
receives, throughout most of its extent, secondary olfactory fibers.
(a) Corpus precommissurale. Extending from the rostral end
of the hemispheres caudally into the diencephalon is a column of
cells, bordering the medial cavity on either side. Its dorsal
limit is indicated by the sulcus limitans telencephali and it is
bounded laterally, throughout most of its more caudal portion, by
the palaeostriatum.
This is the corpus precommissurale ; the area olf actoria posterior
medialis and epistriatum of Kappers, '06, but not of Kappers, '08,
where this name is applied to the primordium hippocampi; the
lobus olfactorius posterior, pars medialis of Goldstein; 'vordere
nucleus,' partly, of Bela Haller. At the rostral end of the hemisphere this nucleus is largely ventral (fig. 25) ; toward the anterior
commissure, however, it increases in dorso-ventral extent covering practically all the mesal surface of each hemisphere (fig. 35).
The interposition of the fibers of the commissure separates the
nucleus into two parts, a dorsal passing above the commissure,
and a ventral composed of cells lying between its fiber systems
(figs. 35, 36, 38, 55, 56, 61). Caudally of the anterior commissure,
these two divisions of the nucleus remain distinct, one continuing
192 RALPH EDWARD SHELDON
ventrally, close to the median cavity, while the other remains
dorsal, meeting the lateral olfactory area in the polus posterior
of the hemisphere, and then continuing caudally under {he habenula. This forking column of cells is, as will be brought out more
clearly later, the morphological equivalent of the precommissural
body or paraterminal body of Elliot Smith in mammals and reptiles, and is, therefore, here termed the corpus precommissurale.
The rostral portion of the nucleus corresponds morphologically
to the rostral part of the ganglion mediale septi of Gaupp, or the
area precommissuralis septi of Kappers and Theunissen in the
frog, and is called, therefore the nucleus medianus (fig. 25).
The portion of the nucleus extending into the commissure is
simply the bed of the anterior commissure of Elliot Smith in
reptiles and mammals and is called, therefore, the pars commissuralis. The arm of the precommissural body arching over the
commissure presents points of resemblance to the pars fimbrialis
septi of Kappers and Theunissen in the frog. It is here called the
pars supracommissurahs (figs. 35, 36, 38, 55, 56, 61). Its extension caudad behind the commissure joining the lateral olfactory
area is named the pars intermedia (figs. 66, 67, 68, 70). The commissure bed passes immediately caudad into a nucleus of small
cells, bordering the ventricle, which is here termed the nucleus
preopticus (figs. 61, 66, 67, 68, 70, 73, 76, etc.). This is composed
of several different cell groups which will be taken up in greater
detail later.
All parts of the corpus precommissurale appear very discrete
in toluidin blue preparations. In the nucleus medianus, the
cells are closely packed, but are arranged in groups or islands
(figs. 25, 26). (See Calleja, '93.) Usually a clear zone of few
cells surrounds the precommissural body particularly dorsally
and laterally (fig. 38). In the pars supracommissurahs the cells
are less closely packed (figs. 38, 46, 56), and have lost the island
arrangement. The grouping in the pars commissuralis, is largely
dependent on the position of the fiber bundles of the anterior commissure; the cells are, however, fairly evenly distributed (figs.
38, 56).
OLFACTORY CENTERS IN TELEOSTS 193
In the rostral part of the commissure bed is found the group
of cells in which terminate the fibers of the nervus terminahs. The
pars intermedia of the corpus precommissurale consists of a
narrow column of cells, fairly closely packed and forming a distinct band across the ventral portion of the posterior pole of the
hemisphere (figs. 66, 67, 68, 70). Its niorphological relationships
are obscure.
In Golgi preparations of different parts of the precommissural
body some of the cellular relations are brought out more fully.
In the nucleus medianus the cells are fairly large, fusiform, pyramidal or ellipsoid in shape, with almost all of their processes coming from the ends of the perikaryon as shown in figs. 28 to 31.
A large proportion of these cells give rise to the fibers of the
tractus olfactorius ascendens. The neurites are very delicate,
possessing granular enlargements along their course. Smaller
cells with a number of short, root-like dendrites and a single long
neurite extending into the palaeostriatum, are not uncommon
(fig. 43) . Several varieties of small cells, apparently functioning
as association cells, are found also in the nucleus medianus;
these are chiefly stellate, or irregularly rounded (figs. 41, 42).
In the pars supracommissuralis the cells are smaller; also rather
more of the association cells of the type shown in figs. 41, 42 are
found. Cells of type shown in fig. 43, sending fibers to the palaeostriatum, are more common than in the nucleus medianus. Many
of the cells of this nucleus send their neurites into the tractus
olfacto-thalamicus medialis. Such a cell is shown in fig. 40. Small
stellate and small pyramidal cells are rather more common than
the type illustrated.
(b) Primordium hippocampi. Dorsad of the sulcus limitans
telencephali, appearing with especial distinctness rostrally, lies
the primordium hippocampi, or nucleus olfactorius dorsalis.
Between it and the corpus precommissurale may be seen a slight
clear area, devoid of cells. The cells of the primordium hippocampi are rostrally slightly smaller than those of the nucleus medianus, while dorsal to the pars supraconamissuraUs they are very
similar to those of the latter nucleus (fig. 46). Many of them
resemble the dorsal cells of the nucleus olfactorius lateralis (figs.
THE JOURNAL OP COMPARATIVE NEUROLOGY, VOL. 22, NO. 3
194 RALPH EDWARD SHELDON
48, 49, 56). The primordium hippocampi receives secondaryolfactory fibers from the tractus olfactorius mediahs and a few
commissm"al fibers associated with the commissura corporium
precommissurahum. The neurites of its cells descend partly
with the tractus strio-thalainicus and partly with the tractus
olfacto-thalamicus medialis, pars dorsalis. No tertiary olfactory
fibers could be traced, in Golgi preparations, either from the
lobus pyrif ormis or the corpus precommissurale to the primordium
hippocampi. In Ram6n y Cajal preparations, however, mingled
with the fibers of the commissura corporium precommissurahum
rostrally are a number of unmedullated fibers connecting the
nucleus medianus with the primiordium hippocampi. From the
conditions in amphibians, reptiles and mammals it seems extremely
probable that these represent the tractus area-hippocampalis rectus
of Kappers and constitute an association path between the precommissural body and the primordium hippocampi. The morphology of this region will be considered more in detail further on.
(c) Nucleus olfactorius lateralis. Laterally, extending from the
extreme rostral end of each basal lobe to the extremity of the
polus posterior, lies the lateral olfactory area; the area olfactoria
of Edinger, the lobus olfactorius posterior, pars lateralis of Goldstein, area olfactoria posterior lateralis of Kappers ('06), area
olfactoria lateralis of Kappers and Theunssen ('08). The nucleus
olfactorius lateralis is here divided into itwo parts, both rostral
to the sulcus ypsiliformis, and consisting of rather evenly distributed, somewhat scattered cells. The more rostral appears
externally as the tuberculum anterius (figs. 2 and 3), while the
more caudal presents superficially the tuberculum laterale. The
nucleus olfactorius lateralis covers as a cap the entire rostrolateral surface of each basal lobe. At the extreme rostral pole it
is restricted to the lateral aspect but passing caudally it gradually
spreads dorsally covering the dorso-lateral aspect of each lobe, at
the level of the sulcus ypsiliformis (figs. 25, 38).
The lobus pyriformis, so named since it is closely related to the
pyriform lobe of mammals, consists dorsally and caudally, of
evenly distributed scattered cells very similar to those of the nucleus olfactorius lateralis (figs. 38, 56, 66, 67) . Ventrally, imme
OLFACTORY CENTERS IN TELEOSTS 195
diately lateral to the fissura endorhinalis, a portion of the nucleus
pyriformis is specialized to form the nucleus teniae of Kappers,
Goldstein, Edinger, the caudal portion of the hypostriatum of
Catois, nucleus occipito-basalis of C. L. Herrick. This is a compact nucleus of rather small cells (fig. 57) . Caudally it meets the
pars intermedia of the corpus precomniissurale, both being covered
dorsally by the unspecialized cells of the lobus pyriformis (figs.
38, 56, 66, 67, 70).
In preparations by the Golgi method, this region is plainly
marked. Throughout the whole lateral olfactory area, near the
periphery of the lobes, one finds cells of the same general type,
with fine processes, lightly spiny, and with small sized perikarya
(figs. 32, 33, 48, 49, 52, 53). The perikarya vary considerably
in shape, flask-shaped cells being most numerous, as shown in
figs. 32, 33, from the rostral portion of the lateral area, figs. 48,
49 from the dorso-lateral part. Occasionally, small pyramidal
cells of the type shown in fig. 53 may be found. Flask-shaped
cells are particularly numerous close to the periphery of each lobe,
with the rounded margin of the perikaryon directed toward the
periphery and most of the processes arising from the mouth of the
flask. A cell of this type is shown in fig. 52. Part of these processes extend laterally along the ventricular margin, while, the
neurite enters the basal forebrain bundle.
The cells of the nucleus teniae vary somewhat from the general
type of the lateral olfactory area neurone but are recognizably
similar. Many of the cells, as shown in figs. 59, 60, possess perikarya more nearly ovoid than flask-shaped; the processes are
fine and bear inconspicuous spines, however, as do the other cells
of the lateral olfactory area. Fig. 58 shows a cell nearly pyramidal in shape.
(d) Palaeostriatum. In the central part of each basal lobe is
a region called by practically all writers on the teleostean brain
the corpus striatum, here termed the palaeostriatum (figs. 25, 38,
56). It is bounded mesially by the precommissural body, dorsally by the primordium hippocampi and on the other sides by the
lateral olfactory nucleus. Practically all parts of it receive
olfactory fibers of the second order and it is largely, therefore, a
196 RALPH EDWARD SHELDON
portion of the mesal and lateral olfactory areas. The cells of the
central part of this area are very large and conspicuous (fig. 44)
and are quite scattered as compared with the cells of other areas of
the basal lobes. In series stained by cytological methods, such as
toluidin blue or thionin, it is easy to demonstrate that there is a
gradual transition from these conspicuous cells to those typical
of the lateral olfactory area.
According to the Golgi method, neurones of the central portions
of the palaeostriatum appear very large, with comparatively
enormous perikarya, and with long, thick, very thorny dendrites
(figs. 50, 51). In shape, the perikarya vary from short, flaskshaped to pyramidal (fig. 45).
There is shown in Golgi preparations the same transition
between the area olfactoria lateralis and the palaeostriatum, as
in toluidin blue or thionin preparations. One may note a gradual
change, in passing from the periphery centrally, from the small,
flask-shaped cells with rather inconspicuous thorns, to the large
cells, with enormous perikarya and thick, thorny processes; moreover, now and then, a cell of the paleostriatal type will be found
close to the periphery, or a small lateral area cell found in the palaeostriatum. A large proportion of the cells of both the lateral
olfactory area and the palaeostriatum send their neurites into the
basal forebrain bundle, the different parts of which will be taken
up later. The neurites of the cells of the nucleus teniae, however,
enter the tractus teniae. Many of the cells of these two areas are
apparently association cells, functioning not only to bring different parts of the same area, but also adjacent areas, such as lateral
olfactory area, palaeostriatum and corpus precommissurale, into
relation. Such is apparently the function of some of the cells of
the type shown in figs. 50, 51.
The word 'paleostriatum' is not used in quite the same sense
as it is used by Kappers, as will be noted from the preceding discussion. Kappers believes that the palaeostriatum is closely connected with the olfactory apparatus, but receives no somatic sensory connections from the thalamus, which it probably does receive
in the teleosts. The term as here used indicates that a structure is
found in the teleosts, closely related to the secondary olfactory
OLFACTORY CENTERS IN TELEOSTS 197
centers, and morphologically related to a part, at least, of the corpus striatum of higher forms.
(e) Nucleus commissuralis lateralis. Situated in the ventromedial portion of each basal lobe, in the region of the anterior
commissure, at either end of the commissure is a small compact
nucleus of fairly large, closely packed cells (figs. 38, 56). No
references to it in the literature have been noted; it has, therefore,
been* termed the nucleus commissuralis lateralis, owing to its
location, laterally at the level of the anterior commissure.
(f) Nucleus preopticus. Immediately caudal to the anterior
commissure there appears ventrally the recessus preopticus of the
third ventricle (fig. 56) . Surrounding this, on either side, and
passing rostrally insensibly into the pars supracommissuralis,
is the nucleus preopticus. This nucleus is composed of cells of
two types; at the level of the caudal margin of the hemispheres is a
dense mass of cells bordering the median ventricle; its cells are some
of the largest in the brain (fig, 71), and are flask-shaped with their
bases directed toward the ventricle and most of their processes
extending laterally and ventro-laterally (figs. 67, 70,71). This is
here termed the pars magnocellularis of the nucleus preopticus.
Rostral to this nucleus, continuous with the pars supracommissurahs, is a nucleus of small cells (fig. 64) , This group of cells
extends caudally, lateral to the pars magnocellularis, gradually
curving around it caudally, thus enclosing the nucleus magnocellularis on three sides. In contradistinction to the nucleus magnocellularis this is called the pars parvocellul?ris of the nucleus
preopticus. To the portions rostral, lateral and caudal to the
pars magnocellularis are assigned the suffixes, anterior, lateralis
and posterior, respectively (figs. 64, 66, 67, 70, 78) . This nucleus
extends caudally to the region of the fibrae ansulatae.
In Golgi preparations the pars parvocellularis shows cells of
several types, resembling closely the various kinds of small cells
of the corpus precommissurale.
The nucleus preopticus was recognized by C. L. Herrick in 1892.
Herrick saw both the large and small cells and applied the name
nidulus praeopticus to the larger portion of the nucleus; it is
probable, however, that his nucleus postopticus contains a por
198 RALPH EDWARD SHELDON
tion of the cells here included under the name nucleus preopticus.
Bela Haller noted the same group of cells and termed it the
nucleus posterior of the forebrain. Johnston ('98) and ('01) found
a nucleus bordering the recessus preopticus and termed it the
nucleus thaeniae owing to the fact that he observed fibers passing
from it to the habenula, and that, therefore, it is ('98) "a nucleus
corresponding to the nucleus occipito-basalis of (C. L.) Herrick
and the nucleus thaeniae of Edinger" in reptiles. This view is
untenable as will be pointed but later. Johnston probably recognized the fact, as he terms it nucleus praeopticus in his 'Nervous
System' ('06). Kappers noted the large cells and, following Herrick, named the group, nucleus praeopticus. Goldstein, following the descriptions of Edinger for the brains of reptiles and birds,
applied the names magnocellularis and parvocellularis strati grisei
to the two components of the nucleus.
(g) Nucleus entopeduncularis. Appearing immediately caudal to the nucleus commissuralis lateralis is a group of very small
cells (fig. 65), lying embedded in the basal forebrain bundle (figs.
66, 67, 68, 70). This is the nucleus entopeduncularis of Goldstein.
3. THE DIENCEPHALON
a. Rostral limits
The division of the vertebrate brain into transverse segments,
with a clear definition of their limits, is a matter of considerable
difficulty, particularly since, as Johnston and C. J. Herrick have
pointed out, most of the important morphological centers and
fiber connections are arranged in longitudinal columns. The
question of the caudal boundary of the telencephalon ventrally
is still unsettled, some authors considering the pedunculi thalami,
caudal to the anterior commissure, part of the diencephalon,
others placing the rostral limits of the 'tween-brain behind the
optic chiasma in the adult. Dorsally the caudal margin of the
velum transversum has long been considered the hmit of the forebrain. Johnston recently ('09) has taken up the subject in some
detail and his interpretation is here followed; according to which
• OLFACTORY CENTERS IN TELEOSTS 199
the caudal limits of the forebrain include the velum transversum
and the optic chiasma. The pedunculi thalami, the praethalamus
of C. L. Herrick, are included in the telencephalon, and their centers have already been described (nucleus preopticus and nucleus
entopeduncularis) .
Most writers on the brains of fishes have, however, included
these structures in the diencephalon ; in fact even under the interpretation here followed, the pars parvocellularis posterior of the
nucleus preopticus extends into the diencephalon, since it reaches
caudally to the level of the fibrae ansulatae.
b. Gross morphology
The diencephalon in the carp is of the typical teleostean type.
Immediately caudal to the velum transversum, the diatela is
thrown into a convoluted folded epithelial sac, extending rostrall}^ over the membranous pallium of the hemispheres, forming
the saccus dorsalis, post- velar arch, or Zirbelpolster (figs. 68, 73).
This is an extremely vascular structure, formed by the covering of
pia mater and a lining, continuous with the ependyma of the third
ventricle. Arising immediately caudal to the saccus dorsalis,
with the caudal wall of the one practically adherent to the rostral
wall of the other, is the epiphysis or pineal body. This is a small
elongated tubular organ extending rostrally, suspended in the
folds of the dorsal sac. Its epithelium, while an extension of that
of the ependyma, is glandular in type. Lying embedded in the
membranous wall between the dorsal sac and the epiphysis, is
found the commissura habenularum, or commissura superior. At
the caudal base of the epiphysis is found the commissura posterior,
between it and the tectum opticum.
The diencephalon is commonly subdivided into epithalamus,
hypothalamus and thalamus. The latter has been divided by
C. J. Herrick ('10), following Ram6n y Cajal, into pars dorsalis
(sensory correlation centers) and pars ventralis (motor correlation
centers) . The epithalamus of the carp is distinct ; the other parts
are so confused that further embryological study will probably be
necessary to effect this separation; and the assignment of the differ
200 , RALPH EDWARD SHELDON
ent nuclei and fiber tracts to these regions in this paper must be
regarded as provisional, particularly with respect to the centers
lying within, and immediately dorsal to, the lateral parts of the
inferior lobes.
The inferior lobes consist of an unpaired pars medialis, which is
clearly hypothalamic, and paired partes laterales, the lateral
lobes, which apparently belong chiefly to the pars ventralis
thalami.
The lobi laterales are widely separated rostrally by the interposed lobus medius, while they meet one another caudal to it.
Caudally a furrow appears on the ventral aspect of the lateral lobes,
the sulcus mammillaris of Goldstein (fig. 4). The prominence of
the lobes mesal to the two sulci, is due to the development dorsally of the corpora mammillaria of Goldstein (fig. 117). Laterally, each inferior lobe shows several lobes and sulci, varying somewhat in different individuals. Rostrally the great size of the
nucleus prerotundus and nucleus rotundus causes the development
of a shght protuberance, appearing on the outside of the lobe (fig.
3). Further caudally the nucleus cerebellaris hypothalami gives
rise to a similar enlargement (fig. 3) . The lobus medius consists
of the tuber cinereum rostrally, and the pars infundibularis
caudally.
Extending ventro-rostrally from the tub-^r is found the hypophysis, consisting of the two conspicuous solid lobes, separated by
a circular constriction; a rostral pars glandularis and a caudal
pars nervosa. Ventrally these are separated into symmetrical
parts by a longitudinal median furrow (fig. 4), Extending caudally from the caudal margin of the pars ii.fundibularis of the lobus
medius is a narrow, thin, glandular, membranous sac, the saccus
vasculosus, opening into the infundibular cavity (fig. 4).
The median cavity of the forcbrain extends caudally and ventrally between the two pedunculi thalami and thalamus proper,
giving rise to diverticula which penetrate the lateral lobes. (For
a more detailed account of the ventricles of the teleostean iiiferior lobes see Goldstein ('05), pp. 189-195, figs. 13-19; Edinger
('08), fig. 171.)
OLFACTORY CENTERS IN TELEOSTS 201
(1) Epithalamus. The epithalamus of the carp is easily defined,
consisting of the saccus dorsahs and epiphysis and the habenular
centers, including the two habenular ganglia, the habenular decussation, or commissure and the nucleus posthabenularis, together
with their connections.
The ganglia habenularum are very conspicuous in the carp,
protruding for half their diameter into the median cavity (figs.
78, 81). Their cells are small and evenly distributed but thrown
into groups or islands by the fibers of the tractus olfacto-habenularis and the fasciculus retroflexus (figs. 78, 81). As seen in Golgi
preparations, the cells are very characteristic, of the type normal
throughout the vetebrate series (fig. 75) .
Nucleus posthabenularis. Immediately ventral to the habenular ganglia, the cells of the one continuous with the cells of the
other, lies the nucleus posthabenularis, 'das posthabenulare
Zwischenhirngebiet' of Goldstein, the 'posthabenulare Zwischenhirngegend' of Bela Haller, Meynert's nucleus of reptiles
(figs. 78, 81). Rostrally, it becomes continuous with the nucleus
intermedius (fig. 70), while caudally it extends beyond the level
of the commissura posterior (fig. 84) always holding a position close
to the median ventricle and ventral to the fasciculus retroflexus.
(2) Thalamus. At the level of the habenulae, there appear on
either side, immediately ventral to the arch of the tectum, the
corpora geniculata lateralia. Mesal to the lateral geniculate
body lies the nucleus anterior thalami of Goldstein (figs. 78, 81).
This is easily recognized, owing to its large size and its characteristic appearance, showing a ring of cells about its periphery (fig.
81).
Nucleus rotundus and associated centers. One of the most
important parts of the thalamus, and at the same time one of the
most difficult to understand in all its relations, is the region of
the nucleus rotundus. Owing to its prominence, it has been noted
by nearly every writer on the teleostean brain. It was described
by Fritsch and called by him the nucleus rotundus ; Bellonci used
the same term, while C. L. Herrick termed it the nucleus ruber.
Goldstein assigns the name nucleus ventrahs thalami to this
202 , RALPH EDWARD SHELDON
whole region, although he shows both in his figures and descriptions that it contains different groups of cells with different characteristics. Kappers ('06) pointed out that the center previously
described as nucleus rotundus is really made up of several characteristic groups of cells. That
situated most dorsally, proximally and laterally, is the nucleus praerotundus. This group .... gradually passes backward into a
much larger group situated under and lateral to the level of the nucleus
rotundus and ending where the real nucleus rotundus has its largest
size. This latter group, which belongs entirely to the lobi inferiores,
I shall distinguish as the nucleus subrotundus from the nucleus rotundus
proprius, as it extends in part under the real nucleus rotundus so that
the com. horizontalis, before it enters the lower border of the latter, lies
for some distance over it and between it and the nucleus rotundus proprius.
This separation of the nucleus rotundus of the earlier authors
into three different components is a matter of considerable morphological importance, as will be brought out later. Kappers'
description applies in a general way to the' relations in the carp,
with some important modifications.
At the level of the rostral margin of the lateral lobes, the nucleus
prerotundus appears ventro-laterally immediately ventro-lateral
to the commissura transversa (fig. 78). It consists here of a
fairly compact mass of irregularly shaped cells of medium size.
A short distance further caudally this nucleus lies wedged in
between the lateral lobe and the commissura transversa. Dorsolaterally it forms a small protuberance on the lateral surface of
the brain (fig. 81). From this point the nucleus prerotundus
extends caudo-mesially to the region of the nucleus posterior
tuberis. It may be compared in shape to the caudate nucleus in
the human brain, with a large and conspicuous head rostrally,
gradually diminishing in size caudo-mesally (figs. 84, 89, 103, 106).
The nucleus rotundus proprius is by far the largest and most
conspicuous nucleus of the thalamic region. It appears rostrally
at about the rostral margin of the commissura posterior and extends caudo-mesally, lateral to the nucleus prerotundus, almost
to the conamissura ansulata, meeting the corpus mammillare
ventro-mesially (figs. 84, 89, 103, 106, 117).
OLFACTORY CENTERS IN TELEOSTS 203
Ventrally of the nucleus rotundus, extending caudo-laterally
from the level of the nucleus posterior tuberis, to the level of the
caudal margin of the corpus mammillare, lies the nucleus subrotundus (figs. 106, 117).
When the three components of the nucleus are considered together, it is noted that the nucleus prerotundus forms a cap over
the rostro-mesal surface of the nucleus rotundus (fig. 84), decreasing in transverse diameter as the latter increases in size (fig. 89).
At approximately the level where the nucleus prerotundus ends,
the nucleus subrotundus is beginning to appear, embedded in the
nucleus rotundus ventro-laterally (fig. 106). Further caudally
(fig. 117), since the nucleus rotundus extends caudo-mesally
while the nucleus subrotundus extends caudo-laterally, the two
come to lie approximately in the same horizontal plane, one lateral
to the other, the nucleus rotundus merging into the dorsal margin
of the corpus mammillare; the nucleus subrotundus similarly
ending in the nucleus cerebellaris hypothalami and losing its
typical shape and appearance (see figs. 136-140, for a horizontal
projection of these nuclei).
In addition to their conspicuous size, the nuclei rotundi show
a characteristic structure, hardly fully brought out in any of the
drawings. The nucleus prerotundus throughout most of its
extent is composed of rather large scattered cells, together with
small numbers of various smaller sized cells (fig. 85) showing
faintly between them. Several of the cells from Golgi preparations
are shown in figs. 86 to 88. The cells of the nucleus rotundus
are smaller and more nearly of the same size. They are always
scattered in groups or islands, giving a characteristic appearance
to the nucleus (fig. 90). Figs. 91 to 94 show several from Golgi
preparations. The nucleus prerotundus and rotundus combined
form the ' kleinzellige' portion of the nucleus ventralis thalami of
Goldstein. The most easily recognizable of these nuclei is the
nucleus subrotundus, owing to its extremely characteristic appearance near its rostral end, or head. There, as shown in figs. 106 and
107, it presents a circular appearance in transection, with its cells
grouped in the center and surrounded by a clear peripheral area.
The cells average larger than those of the remaining two nuclei
204 RALPH EDWARD SHELDON
and are noticeably so in its caudal part, where they become large,
spindle shaped or pyramidal, as the nucleus cerebellaris hypothalami is approached. This nucleus corresponds to the 'grosszellige' portion of the nucleus ventralis thalami of Goldstein.
By the Weigert or Ram6n y Cajal methods the nucleus prerotundus and rotundus show a peculiar blotched appearance, due
to the presence of small bundles of fine fibers scattered between
the islands of cells; fig. 102 brings this out fairly well.
Nucleus posterior thalami. Lateral to the nucleus rotundus,
at the level of the nucleus posterior tuberis, is a nucleus of very
large ganglion cells, the nucleus posterior thalami, the 'Vereinsgebiet' of Bela Haller (figs. 103, 106, 117). This gradually increases in size caudally finally disappearing in the nucleus cerebellaris hypothalami. Its cells are particularly large as shown in
fig. 109 from a toluidin blue preparation and figs. 110 to 113 from
Golgi preparations.
Nucleus ruber tegmenti. Dorso-mesal to the caudal part of
the nucleus posterior thalami, and dorsal to the nucleus subrotundus is a nucleus of extremely large cells, the nucleus ruber
tegmenti of Goldstein (fig. 117).
The remaining centers of the thalami are omitted from consideration in this article as they have no special connection with
the olfactory apparatus and are not necessary for purposes of orientation. This includes the nucleus dorsalis of Goldstein, the nucleus
coriicalis of Kappers, the nucleus praetectalis, and nucleus intermedius of Goldstein.
(S) Hypothala7nus. The hypothalamus consists of the lobus
medius and part of the lobi laterales of the inferior lobes (figs.
3, 4), together with their included centers and connections, and
the hypophysis. The lobus medius consists rostrally of the tuber
cinereum and caudally of the pars infundibularis. Ventro-rostrally, as previously noted, is given off the hypophysis, while
extending caudally from the pars infundibularis, is found the
saccus vasculosus.
Nucleus anterior tuberis. A single group of cells, the nucleus
anterior tuberis, makes up the larger part of the rostral portion
of the lobus medius (figs. 81, 84, 89). This is composed of sniaji
OLFACTORY CENTERS IN TELEOSTS 205
cells, appearing as a core in the center of the nucleus (figs. 84,
89) . Rostrally, the nucleus anterior tuberis is continuous past the
fibrae ansulatae, Herrick's commissure, etc., into the nucleus
preopticus, pars parvocellularis posterior. Caudally, the nucleus
ends at the level of the lateral ventricular diverticula, leading to
the lobi laterales (figs. 100,101). See also Edinger ('08), fig. 171 ;
Goldstein ('05), text-fig. 16.
Nucleus posterior tuberis. Dorsad of the diverticula the nucleus anterior tuberis passes caudally into the nucleus posterior
tuberis, immediately ventral to the tuberculum posterius (Haubenwulst) (fig. 103). This is a nucleus of small cells, similar in
appearance to those of the nucleus anterior tuberis, although its
cells are more evenly distributed.
Nucleus ventralis tuberis. Appearing rostrally, immediately
ventral to the commissura horizontalis, is a nucleus of enormous
cells, not hitherto described in the literature, which is here termed
the nucleus ventralis tuberis (fig. 78). It continues for a short
distance caudally, lying close underneath the median ventricle
and gradually diminishing in size (figs. 81, 84).
Nucleus lateralis tuberis Laterally, appearing immediately
caudal to the commissura horizontalis, at the ventro-lateral margin of the nucleus anterior tuberis, occurs a closely packed group
of large cells, the nucleus lateralis tuberis (fig. 84) . This is found
only for a short distance at the level of attachment of the hypophysis.
Nucleus ventricularis. Close to the median ventricle, particularly as far caudal as its diverticula, may be seen a layer of
densely packed cells close against the ependyma. Similar cells
may be noted adjacent to the median ventricle rostrally, even
before the anterior commissure. The same condition holds
also for the walls of the lateral diverticula into the lobi laterales.
It is noticeable that wherever these cells are found the ependyma
consists of higher columnar cells than in other regions. These
probably belong to the apparatus, described by Johnston, for
the regulation of blood pressure in the brain.
Nucleus diffusus lobi lateralis. Throughout the peripheral
portion of the lobi laterales, particularly laterally and ventrally,
206 RALPH EDWARD SHELDON
is an evenly distributed area of small cells, forming the nucleus
diffusus lobi lateralis of Goldstein, the substantia grisea lobi inferioris of Kappers, who divides it into a pars anterior and a pars
posterior (figs. 78, 81, 84, 89, 103, 106, 117). The cells, as shown
in Golgi preparations, possess elliptical or flask-shaped perikarya,
with many finely spiny dendrites, resembling somewhat the undifferentiated cells of the area olfactoria lateralis. A number of the
cells are shown in figs. 95 to 99. This undifferentiated area is
evidently the primitive structure of the lateral lobes from which
its nuclei have been gradually evolved. (Compare the condition
of ganoids, according ^to Johnston.)
Nucleus cerebellaris hypothalami. Appearing rostrally, at
approximately the middle of the longitudinal extent of the lateral
lobes, occm's a nucleus of large evenly distributed, scattered cells,
the nucleus cerebellaris hypothalami of Goldstein (fig. 89). This
extends caudally and lateralh^' gradually increasing in size until
it occupies a large part of the transverse diameter of each lateral
lobe (figs. 89, 103, 106, 117). It extends practially to the caudal
part of each lobe, laterally. A small area, under high power, is
shown in fig. 108.
Corpus mammillare. The only remaining center of importance
in the lobi laterales is the ganglion mammillare of Goldstein.
Rostrally and dorsallj' it meets the tail of the nucleus rotundus;
thence it extends caudally, always adjacent to the median wall
of the caudal portion of each lobe (fig. 117), practically to the tip
of the lobes. It is composed of very small, closely packed, evenly
distributed cells of characteristic form (figs. 118, toluidin blue;
119 to 121, Golgi). Where this nucleus comes into contact with
the nucleus rotundus the two may be easily distinguished by the
difference in the size and arrangement of the cells.
In Weigert preparations the corpus mammillare is easily distinguished, owing to the large number of fine medullated fibers
found in it, giving it a finely reticular appearance.
A number of the cell groups here introduced will not be further considered but have been mentioned in order to give an
accurate understanding of the relations of the different centers.
OLFACTORY CENTERS IN TELEOSTS 207
4. THE FIBER TRACTS
a. Crural tracts
The olfactory neurones of the first order from the olfactory
mucous membrane to the olfactory bulbs and thek connections
at that point have already been described. The connections
between the bulbs and hemispheres will next be considered. It
has long been known that the fibers of the olfactory tracts pass
between the bulbs and olfactory lobes in two bundles; Bellonci
was the first to divide the tracts into a medial and a lateral.
C. L. Herrick in 1891 brings out clearly tke morphological relations of these two tracts, which he calls the radix lateralis and the
radix mesalis. He points out that the radix lateralis passes
directly from the bulbs to the caudo-lateral part of each basal
lobe, which he terms hippocampus, and that the radix mesalis
decussates in the anterior commissure. Edinger ('96) figures a
horizontal projection of the basal lobes of the carp, in which he
traces the lateral tract, called by him the tractus bulbocorticalis,
into a region termed the area olfactoria, while the median olfactory bundle, or tractus bulbo-epistriaticus, ends partly in the epistriatum of the same side, and partly decussates in the anterior
commissure. Catois ('01) identifies the same two bundles as
'Le faisceau externe' and 'Le faisceau interne.' Catois is the
first to point out that the medial tract consists of both centripetal and centrifugal fibers. He agrees with Edinger that it is
partly crossed and partly uncrossed. Bela Haller likewise identifies the two tracts. Goldstein ('05) has worked out the relations
of the bundles in more detail than his predecessors, and finds that
the lateral tract, 'laterale Riechstrahlung,' originates in the lobus
olfactorius anterior and ends, largely uncrossed, in the lobus
olfactorius posterior, pars lateralis, while a few fibers decussate
in the anterior commissure to end in the same area oh the opposite
side. The 'mediale Riechstrahlung' is formed, according to
Goldstein, entirely from centripetal fibers, which run in several
distinct bundles. The more lateral originates in the lobus olfactorius anterior, and decussates in the anterior commissure to
208 RALPH EDWARD SHELDON
end in the lobus olfactorius posterior, pars lateralis, of the opposite side. The remaining two bundles originate from the formatio
bulbaris; the more medial forms the commissura olfactoria interbulbaris, while the more lateral ends in the lobiis olfactorius
posterior, pars medialis, in which are confused the precommissural
body and the epistriatumof Edinger. Kappers ('06) observes two
different conditions in the teleosts examined by him. The lateral
tract, or radix olfactoria lateralis, always ends in the area olfactoria
posterior lateralis (area olfactoria of Edinger) ; in Gadus, Thynnus
and Lophius it ends on the same side, however, while in Salmo
it decussates in the ajiterior commissure to end in the opposite
side. Kappers also finds that the medial tract is composed of
two parts, a medial tractus olfacto-lobaris medialis and a lateral
radix olfactoria medialis propria. He finds that both sets of
fibers decussate and that most of them end in the area olfactoria
posterior medialis, here termed epistriatum, although a few in
Salmo may end in the lateral area.
In none of the previous work on these tracts in fishes have all
of the connections been brought out. This is undoubtedly due,
in part, to the lack of a detailed study of the olfactory bulb and
in part to a failure to learn the direction of the different components by the use of the Golgi method.
The olfactory crura in the carp, as previously noted, are very
long and in transections at different levels, the apparent number
of tracts varies considerably. In some sections only one or two
bundles will appear, while in others ten or twelve may be seen.
In order to determine the number and relations of these bundles,
plots were made of several complete series of serial sections of the
crura, showing the number of bundles appearing in each section
and their relation to one another. Micrometer measurements
were used to determine the relations in all doubtful cases ; that is
to say, whenever in one section two bundles were found, and
in the next section three, measurements were taken if there was
any doubt as to which of the two gave rise to the third. In this
way, it is possible to determine the number of important fiber
bundles in the crura and by tracing them to their origin and termination, learn their relation to the centers of the bulbs and basal
OLFACTORY CENTERS IN TELEOSTS 209
lobes. Thus it is shown that instead of a radix mediaUs and a
radix lateraHs there are nine distinct fiber bundles running throughout the crura (figs. 123, 124, 22, 23).*
(1) Tractus olfactorius lateralis. The lateral tract, the tractus olfactorius lateralis, consists of three bundles, a pars lateralis,
pars intermedia and pars medialis. These are composed entirely
of centripetal fibers, arising largely from mitral cells of the lateral
part of each bulb. A few fibers, however, arise from stellate
cells more centrally placed (fig. 124). The tractus olfactorius
lateralis, pars lateralis originates, chiefly in this way, from stellate cells of the nucleus olfactorius anterior, a few of its fibers
arising, however, from peripheral mitral cells (figs. 124, 137).
The tractus olfactorius lateralis, pars intermedia is the largest
and most important of the three. Part of its cells of origin lie
in the nucleus olfactorius anterior, while the larger proportion
are mitral cells from the lateral portion of the bulb rostrally and
dorsally (fig. 6) . One small bundle of fibers originates from the
mesal part of the bulb, crossing dorsally to join the main tractus
olfactorius lateralis, pars intermedia (fig. 6). The tractus olfactorius lateralis, pars medialis is small but extends throughout
almost the entire length of the bulb, arising partly from mitral
cells and partly from stellate cells of the nucleus olfactorius
anterior (figs. 6, 124). The fibers of all three portions of the
tractus olfactorius lateralis pass through the crura (figs. 22, 23),
and gradually spread out above the fissura endorhinalis (figs. 24,
35) to end, without decussating, in the lateral olfactory area
of the basal lobes (fig. 137), including all parts of the nucleus
pyriformis and nucleus teniae. Fibers end throughout almost
the entire length of the area, the fibers ending farthest rostrally
arising from the tractus olfactorius lateralis, pars lateralis. All
three tracts, however, give off fibers to all parts of the nucleus
olfactorius lateralis, rostrally of the sulcus ypsiliformis. A larger
proportion of the fibers of all three bundles end farther caudally,
however, in the nucleus pyriformis, beyond the sulcus ypsiliformis, and in the nucleus teniae. Golgi preparations show that
in all cases the fibers bend abruptly dorsad usually branching
at their termination. The termination of the lateral tract in the
THE JOURNAL OF COMPARATIVE XE UROLOGY, VOL. 22, NO. 3
210 RALPH EDWARD SHELDON
basal lobes of the carp is similar, therefore, to its' ending in the
majority of other teleosts; it has been possible, however, to demonstrate fibers from the tractus olfactorius lateralis in the dorsal
and dorso-lateral region of the basal lobes, called by Johnston
('06) the epistriatum. This area is, therefore, simply a part of
the lateral olfactory area.
(2) Tractus olfactorius medialis. The medial olfactory, described by the earlier workers as a single tract, and by the most
recent as two, is really composed in the carp of five bundles of
widely varying relationships (figs. 22, 23, 124, 136, 137).
Tractus olfactorius ascendens. The tractus olfactorius ascendens described by Kappers, in Salmo, Gadus, etc. (radix olfactoria
medialis propria) as a centripetal tract is, in the carp, as shown by
Golgi preparations, a centrifugal bundle, originating from cells
in the nucleus medianu§ (figs. 27 to 31). Catois described the
more medial portion of the medial tract as centrifugal, but other
authors have been unanimous in considering all excepting a few
commissural fibers as centripetal. The fibers of the tractus
olfactorius ascendens gather from all parts of the nucleus medianus
and extend rostrad to the bulb in two bundles which occupy the
middle or intermediate portion of the base of each crus (figs. 24,
23, 22). On reaching the olfactory bulb the fibers gradually
spread out, and end in the nucleus olfactorius anterior (figs. 124,
136).
Tractus olfactorius medialis. Medially in the bulb and crus
is found the tractus olfactorius medialis. This originates almost
entirely from mitral cells and contains the neurites from practically all the mitral cells far rostrally in the bulb ; it may be traced
much farther rostrally than any of the other tracts of the crus.
Throughout most of the bulb three bundles, belonging to this
tract may be identified (for two of them see fig. 6) ; near the caudal
margin of the bulb, however, these three join to form two, which
may be traced separately to their termination in the basal lobes.
The two lateral bundles originate almost entirely from cells at
the extreme rostral end of the bulb, joining to form the tractus
olfactorius medialis, pars lateralis. This can be distinguished
from the tractus olfactorius mediahs, pars medialis throughout
OLFACTORY CENTERS IN TELEOSTS 211
the entire extent of the crura; for a short distance at the rostral
end of the basal lobes the two are so closely joined, however, that
it is difficult to identify them (figs. 24, 34) . As they come into
proximity to the anterior commissure they again separate, the
tractus olfactorius medialis, pars lateralis holding a position
dorsal to its smaller companion tract (fig. 34). From this point
caudad it extends slightly laterad until the anterior commissure
is reached, when it largely decussates at about the middle of the
commissure, to end in the lobus pyriformis of the opposite side
(figs. 35, .36, 55, 137). This agrees with the more lateral portion of the 'mediale Riechstrahlung' of Goldstein but differs
from the conditions observed by Kappers, excepting for a few
fibers in the brain of Salmo. A small number of fibers, however,
as shown by Golgi preparations, leave the tract before its decussation to end in the nucleus preopticus (fig. 137) and the primordium hippocampi. The tractus olfactorius medialis, pars
medialis originates from mitral cells of the medial surface of the
bulb, and extending to the basal lobes, decussates ventral to and
slightly rostral to, the tractus olfactorius medialis, pars lateralis
(figs. 34, 35, 136). This forms the commissura olfactoria interbulbaris of Goldstein, the commissural fibers connecting the
two olfactory bulbs, which have been described by many writers.
In Weigert preparations it appears as if these fibers actually form
a commissure, but when the crossing is examined in Golgi and
Ram6n y Cajal material, it is found that a large part of the fibers
decussate in the commissure and then end almost immediately,
while a few terminate at the commissure, without decussation.
Many fibers terminate, also, in the pars anterior of the nucleus
medianus, the pars supracommissuralis of the corpus preconmiissurale and possibly in the primordium hippocampi of the same
side. It can not be stated with certainty that no fibers pass
around to the opposite bulb; commissural fibers have, therefore,
been indicated on the diagram (fig. 124). Kappers, Edinger,
•Bellonci and others have noted fibers belonging to the medial
olfactory tract, and ending in the hypothalamus. Such an
appearance is likewise common in Weigert preparations, as the
fibers of the tractus olfactoruis medialis, pars lateralis appear
212 EALPH EDWARD SHELDON
to continue in the tractus o] facto- thalamicus medialis. Such a
condition is deceptive, however, as no such fibers could be demonstrated in Golgi or Ramon y Cajal preparations. It is evident
that the Weigert preparations, which fail to show the fine fibers
as they approach their termination, are, therefore, unreliable in
a study of the origin and termination of tracts, or the relations of
two closely associated bundles.
(3) Nervusterminalis. Earlier a group of ganglion cells belonging to the nervus teminalis was described. As shown in fig.
124 the neurites of these cells pass mesad, lying for a distance
between the two bundles of the olfactory nerve, along the mesal
surface of the bulb. This has been demonstrated in Golgi preparations. In Weigert and vom Rath preparations, an unmedullated tract, undoubtedly formed by the central processes of these
ganglion cells, extends from the same region to the hemispheres
(Sheldon, '09, Sheldon and Brookover, '09). Rostrally this
tract lies embedded in the tractus olfactorius medialis, pars medialis (fig. 6), on the medial aspect of the bulb. As it passes caudad
throughout the crus, it still holds approximately the same position
with reference to the tractus olfactorius medialis, pars medialis
(figs. 22, 23). When the rostral part of the basal lobe is reached,
the nervus terminalis gradually turns dorso-laterad through the
tractus olfactorius medialis to lie between that and the tractus
olfactorius ascendens (fig. 24). As the anterior commissure is
reached, the unmedullated fibers separate from their companion
tracts and decussate in the rostral part of the commissure, ending in the rostral portion of the pars commissuralis of the corpus
precommissurale, as described for the nervus terminalis of selachians by Locy, and in Amphibia by Herrick (figs. 35, 136).
(4) Distribution of secondary olfactory fibers in the forebrain.
It will have been noted that secondary olfactory fibers end in a
very large part of the basal lobes. Fibers of the lateral olfactory
tract end throughout the lateral, dorsal and latero-ventral portions of the basal lobes from the rostral end to the lobus pyriformis and nucleus teniae of the-.polus posterior. These fibers
extend, also, into a large part of the central area formerly called
striatum. The mesal tract, the tractus medialis, carries centri
OLFACTORY CENTERS IN TELEOSTS 213
petal fibers to" the nucleus medianus; nucleus supracommissuralis,
nucleus preopticus and the primordium hippocampi, probably
also to the nucleus commissuralis lateralis {tr. olf. med.) ; in addition to further fibers for the lobus pyriformis. The only portions
of the basal lobes which do not receive secondary olfactory fibers
are the nucleus entopeduncularis and, possibly, a small area in the
center of the palaeostriatum. It can not be said with certainty,
however, that this latter area receives no olfactory fibers of the
second order; simply that such were not demonstrated.
h. The anterior commissure
The olfactory areas of the two basal lobes are connected by
four sets of commissural fibers, crossing in five bundles. In the
most rostral part of the anterior commissure are found numbers of
fine fibers, partly medullated and partly unmedullated, bending
sharply dorsad. The unmedullated fibers connect the mesal
portions of the two primordia hippocampi, while the medullated
join similar parts of the partes supracommissurales of the corpus
precommissurale (Sheldon, '09 a, fig. 6). A short distance
caudad, accompanied by unmedullated fibers, is a small commissure of medullated fibers connecting the lateral portions of the
partes supracomixdssurales and nuclei dorsales or primordia
hippocampi (figs. 35, 36). This latter bundle, as it presents
points of resemblance with the commissura pallii anterior of
reptiles, and the rostral portion of the commissura pallii or commissura dorsalis of Amphibia, is termed on the plates, commissura dorsalis. Morphologically, however, the fibers mentioned
thus far are divisible into a commissura hippocampi, pars anterior,
and a commissura corporium precommissuralium, each bundle
consisting partly of each kind of fibers (fig. 138).
At the caudal part of the anterior commissure a few unmedullated fibers pass across to connect the rostral ends of the nuclei
preoptici of the two lobes. This is termed the commissura nucleorum preopticorum (fig. 138).
The commissura dorsalis is closely associated with the decussation of the tractus hypothalamo-olfactorius medialis and also with
214 RALPH EDWARD SHELDON
a fourth commissure, entirely unmedullated, connecting the
ventral parts of the two nuclei pyriformes, and here termed the
commissura hippocampi, pars posterior. Its fibers are closely
intermingled with those of the decussating tractus olfactorii
mediales, partes laterales, distinguishable in Weigert preparations
owing to their lack of medullary sheaths (fig. 138). See also
Goldstein, Taf. 11, fig. 7; Goldstein terms this the commissura
olfactorii internuclearis. This commissure is shaped like a bow,
with either end bent caudally to terminate in the nuclei pyriformes
(figs. 36, 37, 55). This is the hippocampal commissure of C. L.
Herrick, probably also the commissura interolfactoria of Kappers.
This commissure offers points of resemblance with the fibers of the
commissura dorsalis, which connect the two occipital poles in the
frog and with a part of the commissura pallii of Kappers in the
frog.
It will be noticed that, the anterior commissure complex contains two bundles connected with the primordium hippocampi,
and one with the nucleus pyriformis, all of which are probably
represented in the commissura dorsalis, or commissura hippocampi
of amphibians. The morphological significance of the regions
thus connected will be considered later.
These comprise all of the connections of the basal lobes excepting those bringing them into relation with the diencephalon,
together with a few praethalamic connections which will be taken
up later.
c. Diencephalic connections
(1) The tractus olfacto-habenularis. In 1892 Edinger described
for selachians a tract between the basal lobes and the ganglia
habenularum which he called the tractus ganglii habenulae ad
proencephalon, stating, however, the possibiHty that its fibers
might run in the opposite direction. Such a connection was also
indicated by C. L. Herrick, in the same year under the name of
taenia thalami. All recent writers have observed these fibers,
and have shown that they are largely ascending, from the basal
lobes to the habenular ganglia of the epithalamus. Catois
traces the fibers of his tractus olfacto-habenularis from the caudal
OLFACTORY CENTERS IN TELEOSTS 215
part of the hypostriatum (nucleus teniae) to the habenulae;
Kappers and Goldstein make similar observations. Johnston,
however ('98, '01, '02) in Acipenser and Petromyzon finds that
the larger proportion of the fibers ascending to the habenulae arise
from the nucleus preopticus, called by him the nucleus thaeniae
('98, '01, '02) and nucleus praeopticus ('06). Some fibers in Acipenser are traced from the nucleus postolfactorius ventralis and
nucleus postolfactorius lateralis, corresponding largely to the
corpus precommissurale and the area olfactoria lateralis, respectively. It will thus be noted, as Johnston himself pointed out,
that the tractus olfacto-habenularis of Acipenser and Petromyzon
is not the equivalent of that in teleosts, selachians, amphibians,
reptiles and mammals. The conditions as observed in the carp
explain this discrepancy, as in this form the tractus olfactohabenularis is equivalent to both the tractus olfacto-habenularis
of Edinger, etc., and of Johnston (figs. 140, 141, 142).
The tractus olfacto-habenularis of Catois, Edinger, Kappers,
etc., the taenia thalami of Goldstein, appears conspicuously as a
small, heavily medullated bundle, arising from the nucleus
teniae, lateral to the fissura endorhinalis, at the level of the caudal
margin of the anterior commissure. This is here termed the tractus teniae (fig. 55) and corresponds morphologically to the tractus
cortico-habenularis lateralis of C. Judson Herrick in the Amphibia ('10).
It extends iatero-caudad, dorsal to the bundles of the basal
forebrain bundle (figs. 61, 68), where it receives a few unmedullated fibers from the nucleus intermedius, the tractus intermediohabenularis, pars anterior (figs. 140, 141, 142), possibly homologous
to the tr. septo-habenularis of Herrick. Slightly caudal to this
point the tract receives a small number of unmedullated fibers
from the nucleus entopeduncularis, extending dorsad from the
praethalamus. This is termed the tractus entopedunculo-habenularis (fig. 72), and is probably the morphological equivalent
of the lateral praethalamic portion of the taenia thalami of
amphibians and reptiles. A large part of these fibers may be
descending, corresponding to the tr. habenulo-thalamicus of Herrick ('10). Quite a number of fine unmedullated fibers arise
216 RALPH EDWARD SHELDON
from the nucleus preopticus, pars parvocellularis anterior, to
join the main .tract (figs. 73, 141, 142), termed the tractus preoptico-habenularis, pars anterior. Where the nucleus intermedins
becomes continuous with the nucleus posthabenularis, it gives off
a few unmedullated fibers to the tractus olfacto-habenularis, the
tractus intermedio-habenularis, pars posterior (figs. 141, 142).
The pars magnocellularis gives rise to two sets of fibers for the
habenulae, both unmedullated, a diffuse fiber connection extending dorsad, close to the median ventricle, the tractus preopticohabenularis, pars medialis (fig. 73), and a small compact tract,
which passes lateral to the basal forebrain bundle, the tractus
preoptico-habenularis, pars lateralis (figs. 74, 141, 142). Further
caudally tracts join the main bundle from the pars parvocellularis, pars posterior, of the nucleus preopticus, the tractus preoptico-habenularis, pars posterior; and from the nucleus posthabenularis, the tractus posthabenulo-habenularis (figs. 141, 142).
Part of this may also be descending and, therefore, homologous
with the tractus habenulo-thalamicus of Herrick.
All of these fibers make up the tractus olfacto-habenularis.
It will be noted that the only medullated bundle is the tractus
teniae; this is likewise the most conspicuous of the different fiber
systems which probably explains why it is the only one previously described in teleosts. The habenular ganglia, then, receive
fibers from practically all parts of the caudal portions of both the
lateral and medial olfactory columns. Laterally, fibers pass up
from the nucleus teniae of the lobus pyriformis, medially from the
nucleus preopticus, nucleus intermedins, nucleus entopeduncularis
and nucleus posthabenularis. The lateral connection is the one
observed by Edinger, Catois, Kappers, Goldstein, etc., while the
medial is that found chiefly in Acipenser and Petromyzon by
Johnston. Apparently the largest bundle in Petromyzon corresponds with the tractus preoptico-habenularis, pars lateralis,
in the carp.
Practically all of the fibers of the tractus olfacto-habenularis
decussate in the commissura habenularis, the commissura superior
of many writers (figs. 76, 141, 142). It is possible that a few fibers
end on the same side. It is likewise possible that there are a few
OLFACTORY CENTERS IN TELEOSTS 217
commissural fibers connecting the two nuclei teniarum, taking
this course, and running in the tractus teniae (Edinger ('08) fig.
231), as in the Amphibia. Such fibers would be comparable with
the commissura pallii posterior (commissura aberrans) of lizards.
Several different fiber systems arising from cells in the habenular
ganglia have been described. As indicated above, Edinger, in
his earlier work, believed that the tractus teniae arose in the habenulae, the tractus ad proencephalon. He also describes in selachians a tract to the inidbrain roof, the tractus ganglia habenulae
ad mesocephalon dorsalis ; a tract to the midbrain base, the tractus descendens ganglii habenulae, in addition to the long known
Meynert's bundle, or fasciculus retroflexus, more recently described by Goldstein, Edinger, etc. under the name 'tractus habenulo-interpeduncularis.' Bela Haller observed fibers arising in
the habenulae and entering the optic apparatus, 'Habenularwurzel des Opticus;' also a tract extending ventrad into the diencephalon, ' Hauben-Zwischenhirnbahn.'
(2) Fasciculus retroflexus. The fasciculus retroflexus in the
carp is a strong, chiefly unmedullated tract, originating partly
from cells of the habenulae (fig. 75) and partly from the nucleus
posthabenularis, as pointed out earlier by Bela Haller and Goldstein (figs. 141, 142). From this point it extends caudad to the
corpus interpedunculare, as described by practically all writers
on the habenular connections (figs. 77, 79, 80, 82, 83, 100, 101, 102,
114, 115, 116, 122). As noted by Goldstein, it is surrounded by
medullated fibers caudally. These originate from the nucleus
posthabenularis and pass caudad to the commissura ansulata,
which they appear to enter, turning laterad. Goldstein simply
figures these fibers, giving no description of their connections.
(5) Tractus habenulo-diencephalicus. This tract arises in the
habenulae and, descending into the more ventral diencephalic
regions, is easily identified in the carp, as it is heavily myelinated.
Haller traces it into the nucleus posthabenularis, while Goldstein thinks that it ends farther ventrally, possibly in his nucleus
dorsalis. The tract, according to the conditions in the carp,
contains both ascending and descending fibers and extends ventrocaudad from the habenular ganglia practically to the nucleus
218 EALPH EDWAKD SHELDON
posterior tuberis. (Tractus habenulo-diencephalicus, figs. 77,
79, 80, 82, 83, 100, 101.) Excepting its most rostral part, it is
closely associated with the medial forebrain bundle dorsally,
which probably accounts for the rarity with which it has been
reported. Apparently most of its fibers decussate in the habenular commissure, but such could not be demonstrated with certainty.
The tractus habenulae ad prosencephalon of Goldstein, the tractus ad proencephalon of Edinger, was not identified. Of course,
it is quite possible that some of the fibers of the tractus olfactohabenularis are ascending, as Goldstein believes.
No optic connections with the habenulae could be found, as
Bela Haller describes. Large numbers of cells lying in the nucleus posthabenularis, particularly near the median ventricle,
give rise, however, to fibers which pass directly laterad to enter,
apparently, the optic apparatus as Haller notes (figs. 76, 77, 79,
83). These require further study. Considering the intimate
relation between the nucleus posthabenularis and the ganglia
habenularum, an optic connection, such as Haller describes, not
improbably exists in some forms.
(4) Posthahe^iular-jjreoptic connections. In addition to the
connections already described with the fasciculus retroflexus and
the optic apparatus, the nucleus posthabenularis is placed in
relation with the nucleus preopticus through three sets of diffuse
unmedullated fibers, a tractus preoptico-posthabenularis, pars
anterior from the nucleus magnocellularis to the nucleus posthabenularis; a tractus preoptico-posthabenularis, pars posterior
from the nucleus parvocellularis posterior, and the tractus posthabenulo-preopticus from the nucleus posthabenularis to the
nucleus parvocellularis posterior (fig. 140).
It is evident from its position and connections that the nucleus
posthabenularis is closely related with the habenulae. The two
are evidently a morphological entity, the habenular ganglia developing as specialized portions of the dorsal lamina of the thalamus.
{5) Epiphyseal fibers. Along the caudal wall of the epiphysis
runs a small medullated bundle, which extends caudad to the
posterior commissure. It is possible that it gives off fibers to the
OLFACTORY CENTERS IN TELEOSTS • 219
habenular ganglia as it passes them, but such could not be demonstrated with certainty.
(6) Fasciculus medialis hemisphaerii. This was observed first
by Bellonci in Anguilla, and by him considered to be an olfactory
tract of the second order from the olfactory bulbs to the nuclei
rotundi. The question of the presence of such fibers in the carp
has already been discussed. Edinger similarly traced a part
of the fibers of the medial olfactory tract to the diencephalon,
the tractus ad lobum inferiorem. C. L. Herrick identified the
tract, but states that it originates in the mesaxial lobe (nucleus
medianus and nucleus supracommissuralis of the corpus precommissurale), decussates as the axial commissure (anterior commissure), and then extends to the infundibulum. Herrick calls
the rostral end the 'basal cerebral fasciculus,' while the diencephahc part he terms the fornix tract. Johnston ('98) describes
the bundle as the tractus strio-thalamicus ventralis, passing caudad, without decussation, to end in the inferior lobes. In 1901
he points out that these fibers are largely descending, originating
chiiefly from the nucleus postolfactorius ventralis and to a less
extent from the nucleus preopticus. It also contains ascending
fibers from the corpus mammillare, most of which decussate in
the anterior commissure to end in the epistriatum of the opposite
side. Kappers describes the bundle in the teleosts as originating
in his epistriatum (corpus precommissurale) and ending uncrossed
immediately lateral to the nucleus rotundus. Goldstein gives
the same origin for the fibers, but states that they decussate in the
nucleus posterior tuberis. He notes also that the tract consists
of more than one bundle, but fails to observe any difference in
the connections of the different components.
A careful study of this tract in the carp shows that, instead of
being a simple, single tract, it is really a complex of six fiber bundles each with a distinct course and connections. It likewise
becomes apparent that Kappers, Goldstein, Johnston, etc.,
observed only a part of these components, which accounts for
the differences in the course and connections of the tract as
described by them.
220 • RALPH EDWARD SHELDON
The medial forebrain bundle first appears rostrally at the level
of the anterior commissure, on either side of the mid-line. Immediately dorsal to the commissural fibers appears the tractus
hypothalamo-olfactorius medialis, made up largely of fine, medullated fibers, between which are found many unmedullated in
character (fig. 37). All of the fibers of this bundle are ascending,
originating in the nucleus posterior tuberis (figs. 102, 104). Part
of them decussate almost immediately, as shown in fig. 102, while
the majority pass up on the same side to decussate in the anterior
commissure, closely associated with the fibers of the commissura
hippocampi, pars posterior and commissura dorsalis. Both sets
of fibers terminate in the corpus precommissurale, largely in the
pars supracommissuralis. This tract is that observed by Goldstein caudally, and called by him a descending tract.
Ventral to the fibers of the anterior commissure, at its level,
may be seen another component of the median forebrain bundle,
the tractus olfacto-thalamicus, pars ventralis (figs. 36, 37). The
fibers making up this bundle appear very similar to those of the
tractus hypothalamo-olfactorius medialis. They originate from
the corpus precommissurale, largely in the pars supracommissuralis, and run caudo-ventrad, in a diffuse bundle, to terminate
in the nucleus rotundus and the nucleus posterior thalami.
At the caudal margin of the anterior commissure a third component, the tractus olfacto-thalamicus, pars dorsalis, appears.
This is a rather diffuse bundle, made up of fine medullated and
intermingled unmedullated fibers, which originate largely in the
supracommissural part of the precommissural body and terminate
in the nucleus subrotundus. This bundle, together with the pars
ventralis, was noted by Goldstein, rostrally (Taf. 11, fig. 7).
He points out that one passes doi sal and one ventral to the tractus
olfactorius medialis, pars lateralis, and that both originate in the
medial olfactory nucleus. Apparently, however, he failed to
follow all the fibers caudad, as in the more caudal region he observed only the tractus hypothalamo-olfactorius medialis, which
tract he had not seen farther rosti-ally. The two parts of the
tractus olfacto-thalamicus form the ti-actus olfac^to-hypothalami
OLFACTORY CENTERS IN TELEOSTS 221
cus medialis of Kappers, who failed to note the bundle from the
nucleus posterior tuberis.
A short distance caudal to the anterior commissure, the medial
forebrain bundle has increased largely in size (figs. 68, 69), due to the
presence of a large number of short fibers, most of which are
unmedullated. These are present throughout most of the extent
of tract and are both ascending and descending, connecting and
placing in relation the different parts of the precommissural
body, nucleus preopticus and diencephalon. These fibers form
the tractus olfacto-thalamicus, pars intermedia and tractus thalamo-olfactorius, pars intermedia (fig. 136).
Another factor in the increase in size of the median bundle
consists in the addition to it of a few medullated fibers arising
from the dorso-lateral part of the nucleus magnocellularis, forming the tractus preoptico-tuberis. These pass caudad mingled
with the median forebrain bundle and end, apparently, partly
in the nucleus posthabenularis, and partly in the nucleus posterior
tuberis. These fibers may correspond to the 'Langsbiinder
of Goldstein.
Slightly caudal to the level of the habenulae a seventh tract
becomes closely associated with the median bundle, appearing to
be a part of it. This is the tractus habenulo-diencephalicus of
Goldstein and has already been described in connection with the
habenular tracts (fig. 77).
When a careful study of the median bundle at different transsection levels is made, it is a simple matter to identify its components. Their relations rostrally have already been noted; as
the tract is followed caudad it will be seen that there is a tendency
for the longer components to arrange themselves in more compact
bundles, with the more recently acquired fibers scattered about
them (figs, 73, 74, 76). For some distance there is little change in
the bundle (figs. 79, 80, 82). At the level shown in fig. 83, however, it will be noted that the fibers of the tractus olfacto-thalamicus, pars intermedia and tractus thalamo-olfactorius, pars intermedia, are decreasing in number. The remaining bundles of the
complex are, at this point, separating from one another, all, however, turning ventrad (figs. 100, 101). The tractus habenulo
222 RALPH EDWARD SHELDON
diencephalicus can be traced only a short distance caudal to the
level shown in fig. 101, where it ends mesal to the nucleus rotundus at the level of the nucleus posterior tuberis. The tractus
hypothalamo-olf actorius medialis holds a position near the median
hne.at this point, while the tractus olfacto-thalamici, pars dorsalis and pars ventralis are looping ventro-laterally, to pass below
the nucleus rotundus (fig. 101) to their termini in the nuclei subrotundus and posterior thalami, respectively (figs. 115, 116, 122,
139).
(7) Fasciculus lateralis hemisphaerii. This has been known
from the time of the first workers on the microscopic anatomy of
the teleostean brain. It has been called by various names since
the time of Stieda: pedunculus cerebri, by the earher workers,
' basale Vorderhirnbiinder by Edinger, ' f aisceau basal' by Catois,
'tractus strio-thalamicus' by Johnston, Goldstein, Kappers, etc.
In practically all forms it consists almost entirely of unmedullated fibers, although it is one of the largest and most constant
bundles of the brain. Earlier workers considered that it was made
up exclusively of descending fibers from the cells of the corpus
striatum, ending in the diencephalon. Edinger ('88) states
simply that the fibers originate in the ' Stammganglion' and end
in the ventral part of the ' Zwischenhirn.' He thinks it very likely
that part of the fibers decussate in the anterior commissure.
C. L. Herrick ('91 and '92) divides the basal forebrain bundle
into two parts, both descending, a ventral peduncle arising from
the rostral part of each basal lobe and ending in the caudal part
of the hypoaria, and a dorsal peduncle originating in the caudal
part of each lobe, and ending largely in the nucleus ruber and subthalamicus (nucleus rotundus, sensu lato). Johnston ('98) identifies three sets of fibers in the bundle, a tractus strio-thalamicus
medialis, lateralis and ventralis. Johnston here includes under
the name tractus strio-thalamicus ' ' all fibers connecting the forebrain with the ventral portion of the diencephalon." His tractus
strio-thalamicus ventralis is evidently a part of the medial fore})rain bundle, as is also a portion of the tractus strio-thalamicus
medialis, consisting of ascending fibers from the thalamus to the
epistriatum, decussating in the anterior commissure. John
OLFACTORY CENTERS IN TELEOSTS 223
ston's tractiis strio-thalamicus lateralis arises from cells of the nucleus postolfactorius lateralis, while the larger part of the tractus
strio-thalamicus medialis afises from the striatum proper. In
1901 Johnston modifies these descriptions somewhat. He says
that the ventral bundle is composed of ascending fibers, as noted
above, which end in the epistriatum of the opposite side, together
with descending fibers from the nucleus preopticus. He further
adds that most of the ascending fibers arise from the dorsal and
lateral walls of the mammillary bodies, and run in the medial
bundle. Van Gehuchten ('94) also describes ascending fibers in
the tractus strio-thalamicus, stating that the bundle is made up
of two kinds of fibers, those which originate in the basal ganglia
and end in the inferior lobes, and vice versa. Catois observed
these same two fiber groups one of which is formed by 'fibers
motrices descendantes,' the other by 'fibres sensitives ascendantes.' Catois states that the descending fibers lie external and
dorsal to the ascending. The descending fibers he traces largely
into the nucleus rotundus, and also farther ventrally, while a few
fibers extend into the basal portion of the mesencephalon. The
ascending fibers are traced by Catois from the region of the infundibulum, chiefly from the more rostral part. Catois includes
here the medial forebrain bundle as a part of the tractus striothalamicus. Kappers traces the tractus strio-thalamicus from
all parts of his striatum into the pedunculi thalami, ending uncrossed partly in the nucleus rotundus, but chiefly in the nucleus
subrotundus. Kappers has, however, identified a tract arising chiefly from the lateral olfactory area, the tractus olfactohypothalamicus lateralis, which has been included with the tractus
strio-thalamicus by other authors. This passes caudad, lying
immediately dorsal to the tractus strio-thalamicus, and ending
after decussation in the ventral portion of the inferior lobes. Goldstein has worked out the connections of the tractus strio-thalamicus in considerable detail and finds that it originates from all
parts of the striatum and that part of its fibers decussate in the
anterior commissure, as Edinger suggested in 1888. Goldstein
states that the crossed fibers lie mesal to the uncrossed, and that
the more dorsal fibers in the praethalamic part of the tract contain
224 RALPH EDWARD SHELDON
chiefly fibers from the more rostral part of the striatum. He
traces strio-thalamicus fibers into the nucleus anterior thalami,
nucleus dorsalis thalami, nucleus ventralis thalami, nucleus posterior thalami, nucleus anterior tuberis, nucleus lateralis tuberis,
nucleus diffusus lobi lateralis. The tractus strio-thalamicus of
Goldstein includes the tractus olfacto-hypothalamicus lateralis
of Kappers. Johnston ('02) in Petromyzon states that the tractus strio-thalamicus is formed from the neurites of the cells of the
striatum which end in the central gray of the thalamus. He
also identifies fibers from the lateral olfactory centers, forming a
part of his tractus olfacto-lobaris, which correspond to the tractus
olfacto-hypothalamicus lateralis of Kappers.
As described here, the lateral forebrain bundle consists of the
tractus strio-thalamicus, tractus thalamo-striaticus, tractus olfacto-hypothalamicus lateralis and tractus hypothalmo-olfactorius
lateralis (fig. 139). Rostrally distributed through the central part
of each lobe, almost at the tip of the basal lobes, may be seen
in Weigert preparations many bundles of unmedullated fibers.
Caudally, near the level of the anterior commissure, these bundles
pass gradually ventrad, lying dorsal to the fissura endorhinalis
(fig. 34). Thence these turn slightly mesad (fig. 35), constantly
increasing in size through the accession of new fibers, until at the
caudal level of the commissure the lateral forebrain bundle appears
as a powerful tract containing many large bundles of mixed medullated and unmedullated fibers (fig. 36). As a usual thing the
medullated fibers either form a sheath for the unmedullated or
else form separate bundles, the two kinds of fibers being rarely
intermingled in the same bundle. A large part of the fibers, as
Goldstein describes, decussate in the caudo-ventral part of the
anterior commissure (figs. 36, 37). Caudal to the commissure,
the different bundles become more compactly arranged and extend
through the pedunculi thalami close against their lateral margins
(figs. 55, 61, 68).
The components of the tract, as it passes through the pedunculi
thalami, are shown in fig. 139. It will be noted that the fibers
are both ascending and descending and that the several bundles
have somewhat different connections. In general it may be stated
OLFACTORY CENTERS IN TELEOSTS 225
that the fibers connected with the more rostral part of the basal
lobes lie ventrally and medially; that those belonging to the midportion of each lobe hold an intermediate position, while the more
caudal fibers appear dorsally in the praethalamic bundle. It
will be noted, also, that those which decussate in the anterior
commissure are among the more caudal fibers, while those of the
extreme caudal tip of the basal lobes occupy the extreme dorsal
position and form the lateral hypothalamic tracts (figs. 36, 37,
55, 61, 68, 69, 72, 73).
The lateral forebrain bundle receives from, or sends fibers to,
all parts of the basal lobes excepting the corpus precommissurale,
nucleus medianus, nucleus supracommissuralis, primordium hippocampi, and possibly the nucleus preopticus. The fibers from
the caudal part of the lobes belong to the nucleus pyriforrais
chiefly, although a few fibers are undoubtedly in connection with
the lateral part of the nucleus intermedins; they, therefore, form
a tract corresponding to the tractus olfacto-hypothalamicus lateralis of Kappers. Kappers, however, described this as a descending tract, while it here contains both ascending and descending
fibers, which reach all parts of the nucleus pyriformis (figs. 69,
72).
A large part of the fibers of the tractus strio-thalamicus, or
remaining portion of the lateral forebrain bundle, are ascending
and are distributed to all parts of the palaeostriatum, nucleus
olfactorius lateralis, including the dorso-lateral area of the basal
lobes, called epistriatum by Catois and by Johnston ('06). Many
of these ascending fibers enter into relation with large association
cells of these areas, their neurites enclosing the perikarya of the
cells (figs. 49, 50, 51). Other ascending fibers reach the peripheral
area and branch dichotomously to form tangential fibers (fig. 39),
here coming into relation with the association cells and their
processes. Descending fibers of the tractus strio-thalamicus arise
from cells found in all parts of the same areas, palaeostriatum,
nucleus olfactorius lateralis, etc., already described. The nucleus
olfactorius lateralis, and most, if not all of the palaeostriatum
receive secondary olfactory fibers, while the palaeostriatum
receives also processes from association cells of the corpus pre
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3
226 RALPH EDWARD SHELDON
comniissurale (figs. 39, 139, fib. precoin. str.). So far as the fiber
connections are concerned, therefore, a definitely hmited corpus
striatum in the basal lobes can not be found, thus agreeing with
the relations as shown by a cytological study.
In the pedunucli thalami, as was noted earlier, the fibers of the
lateral forebrain bundle enclose the nucleus entopeduncularis,
giving off collaterals to it (figs. 68, 69, 72, 139).
Throughout the extent of the peduncuh thalaini little change
takes place in the bundle; as it passes over the chiasma its components extend slightly ventrad, however, and now cover all of
the lateral surface of the peduncles (figs. 73, 76). At the rostral
margin of the lateral lobes the more ventral bundles become
closely massed against the commissura transversa (figs. 77, 79),
caudal to which they bifurcate, a few fibers entering the nucleus
anterior tuberis (fig. 80), while many turn into the nucleus prerotundus (figs. 80, 82, 83, 100). The larger proportion of these
two sets of fibers are ascending as Catois states (figs. 104, 105),
although a part are certainly descending. Farther caudally the
intermediate fibers of the bundle likewise turn ventro-laterad and
enter the caudal part of the nucleus prerotundus, passing through
it to distribute along the rostro-mesal aspect of the nucleus rotundus and to the ventral part of the nucleus diffusus lobi lateralis
(fig. 83). Part of the nucleus prerotundus fibers are ascending,
but a definite statement can not be made regarding those of the
nucleus rotundus. In the latter case there is no doubt but that
most of them are descending as C. L. Herrick, Catois and others
describe, although the intermediate bundles certainly contain
some ascending fibers. The fibers break up in the nucleus prerotundus and rotundus in a very characteristic manner, noted by
the earlier workers on the teleostean diencephalon (see C. L.
Herrick ('92), nidulus ruber). This was mentioned earlier and is
shown in fig. 102. The dorsal bundles distribute caudally a few
fibers to the nucleus subrotundus, nucleus posterior thalami,
nucleus cerebellaris hypothalami and a large number to the nucleus difiusus lobi lateralis, ventrally and caudally. The tractus
olfacto-hypothalamicus lateralis has practically the same distribution excepting that it sends no fibers to the nucleus subro
OLFACTORY CENTERS IN TELEOSTS 227
tundus. These fibers are both ascending and descending, although
most of the ascending fibers apparently arise from the nucleus
diffusus. It is difficult to make positive statements regarding the cells of origin of the dorsal ascending fibers of the basal
forebrain bundle owing to rather poor Golgi impregnations of
adult brains in this region (fig. 139) ; there is no question as to
their presence, however, as many such fibers can be seen leaving
these bundles rostrally. In Golgi preparations of the brains of
j'-oung carp fibers may be traced, nevertheless, from a nucleus
apparently corresponding to the nucleus cerebellaris hypothalami
into the tractus strio-thalamicus.
No strio-thalamicus fibers could be traced into the nucleus dorsalis, nucleus anterior thalami or nucleus lateralis tuberis, as Goldstein found in the forms studied by him. It is probable that the
fibers which Goldstein traces into the nucleus lateralis tuberis really
arise from the nucleus magnocellularis, as will be shown later. It
will thus be seen that the lateral forebrain bundle contains throughout, both ascending and descending fibers connecting all of the
lateral and intermediate portions of the basal lobes with practically all of the lateral and intermediate regions of the thalamus
and hypothalamus, and also a part of the medial centers. It is
not, therefore, the simple tract described by the earlier writers,
but a complicated connection of paramount importance to the
nervous mechanism.
(8) The nucleus preopticus and its connections. The fiber
connections of this nucleus have been little understood by the
different writers on the brains of the lower vertebrates. Johnston ('98), as noted earlier, traced fibers from it to the habenular
ganglia; he also believed that secondary olfactory fibers terminate therein, although he could not demonstrate their presence.
Johnston also observed fibers passing caudad, but could not
trace them to their destination. In 1901 he observed fibers from
it entering the tractus strio-thalamicus ventralis (tractus olfactothalamicus, probably pars intermedia). C. L. Herrick ('92)
describes unmedullated fibers from the pars magnocellularis
(nidulus praeopticus) , which pass laterad into the optic tract
region. Kappers notes similar fibers, which he traces ventro
228 RALPH EDWARD SHELDON
laterad, and thence caudad into the tuber cinereum, and terms
the tractus praethalamo-cinereus. Goldstein traces fibers from
the pars magnocellularis caudo-dorso-laterad into 'Das posthabenulare Gebiet/ the 'Langsbiindel des grosszelUgen Kerns
des zentralen Hohlengraues.' From the pars parvocellularis a
few fibers decussate ventrally to enter the nucleus of the opposite
side, the 'Commissur des kleinzelligen Kerns,' evidently the functional equivalent of the commissura anterior, pars preoptica,
previously described (fig. 138). He also finds other fibers
which turn caudo-lateral, dorsal to the chiasma and postoptic
commissures and end among the cells of the caudal portion of the
nucleus in the rostral part of the hypothalamic wall. These
fibers lie lateral to the fibers from the pars magnocellularis, and
mesal to the lateral forebrain bundle. Goldstein believes that
they constitute ein Langscommissur der einzelnen Abschnitte
des kleinzelligen Kernes des zentralen Hohlengraues." He likewise believes that these fibers are identical with the tractus praethalamo-cinereus of Kappers and the caudal fibers of Johnston in
Acipenser. Bela Haller finds a part of these fibers, but believes
that they are connected with the optic apparatus.
It was pointed out earlier that in the carp there are four dift'erent habenular connections from the nucleus preopticus, corresponding partly to the connections described by Johnston in Acipenser and Petromyzon, Olfactory fibers of the second order
may be traced into both the pars parvocellularis anterior and pars
magnocellularis, from the tractus olfactorius medialis, pars lateralis, just before its decussation. This agrees with Johnston's
conjecture (figs. 137, 139, 141). Unniedullated fibers arising from
cells in the nucleus medianus and pars commissuralis of the precommissural body respectively also extend caudad, placing these
two areas in relation with the different parts of the nucleus preopticus (fig, 140, tr. med. preopt. pars ant. and tr. med. preopt., pars
jjost.). The fibers of the tractus mediano-preopticus, pars anterior pass caudad, ventral to the crossing bundles of the anterior
commissure (figs. 37, 54). From it and from the tractus medianopreopticus, pars posterior fine fibers pass ventrad to end in either
OLFACTORY CENTERS IN TELEOSTS 229
side or ventral to the recessus preopticus (figs. 54, 61). These
are probably homologous with the 'Langsfasern des kleinzelligen
Kerns' of Goldstein and are, perhaps, concerned with the movement of cerebro-spinal fluid.
Immediately ventral to the recessus preopticus Goldstein figures and describes a small tract (Taf. 11, fig. 7), the connections
of which he was unable to identify. Fig. 62 shows a parasagittal
section in which the relations of this tract are clearly shown (tr.
preopt. sup.). It is entirely unmedullated and arises from small
stellate cells (fig. 63) immediately ventral to the recessus preopticus, terminating partly in the nucleus parvocellularis posterior
and partly in the nucleus magnocellularis.
The most important longitudinal caudal connection of the
nucleus preopticus is the large unmedullated tractus praethalamocinereus. This originates largely from the nucleus magnocellularis as described by C. L. Herrick and Kappers, the fibers extending latero-ventrad (figs. 72, 73, 76). A part of the fibers, however,
originate from cells of the nucleus intermedins and nucleus parvocellularis anterior (figs. 69, 72), while a few arise in the nucleus
parvocellularis posterior (fig. 76). At first, the tract lies near
the median line (figs. 69, 72, 73) but it gradually turns ventrolaterad (fig. 74) to he ventral to the lateral forebrain bundle
(figs. 76, 77, 79). As it is unmedullated and, therefore, of the
same color as the tractus strio-thalamicus fibers, it is easily mistaken for a part of that tract and was undoubtedly so considered
by the earher authors. Immediately caudal to the postoptic
commissures it bends ventro-mesad, entering the nucleus lateralis
tuberis (fig. 80), where undoubtedly some of its fibers terminate,
and where it probably also receives accessions. Goldstein describes and figures this tract but apparently considers it a part of
the tractus strio-thalamicus, as he traces the latter tract, but not
the former, into the nucleus lateralis tuberis. From this nucleus
the tract extends ventrad into the nucleus ventralis tuberis (fig.
80) where it doubtless undergoes the same change as in the nucleus
lateralis tuberis, thence passing on into the hypophysis, of which
it forms the chief innervation, to terminate particularly in the
230 RALPH EDWARD SHELDON
pars glandularis (figs. 80, 82). Kappers traces this tract, as was
previously noted, only as far as the region of the nucleus lateralis
tuberis, which he fails to identify.
The Langsbiindel des grosszelligen Kerns des zentralen Hohlengraues" of Goldstein could not be identified with certainty. In
sagittal sections a few medullated fibers arising from the dorso-lateral cells of the nucleus magnocellularis could be observed to pass
caudad, closely associated ventrally with the medial forebrain bundle as was noted earlier, apparently ending in the nucleus posterior
tuberis land the nucleus posthabenularis (figs. 136, 140, tr. preopt.
tub.). Medullated fibers extending latero-caudad as Goldstein
describes were not found. It is possible, however, that the unmedullated fibers of the tractus preoptico-posthabenularis, pars
anterior may correspond to Goldstein's tract.
In addition to its longitudinal and habenular connections, the
nucleus preopticus possesses a number of important short transverse, or dorso- ventral connections, all of which are composed of
unmeduUated fibers. Rostrally there are short connections,
running in both directions between the nucleus parvocellularis
anterior, and both the nucleus intermedins and nucleus commissuralis lateralis, the tractus preoptico-intermedius, pars anterior;
intermedio-preopticus, pars anterior; preopticus lateralis; lateralis preopticus (figs. 68, 69, 140). Further caudally are found connections between the nucleus magnocellularis and the nuclei intermedins and entopeduncularis. The nucleus intermedins connections include a double tract medially (figs. 72, 137, 140, tr. preopt.
intermed., pars med. and tr. intermed. preopt., pars med.) and an
ascending tract passing dorsad, lateral to the lateral forebrain
bundle, the tractus preoptico-intermedius, pars lateralis (figs.
69, 72, 137, 140). The short entopeduncular connections are
shown in figs. 69, 72, 140, tr. preopt. entoped. and tr. entoped. preopt. Caudally the nucleus parvocellularis posterior and the nucleus magnocellularis are related to the nucleus posthabenularis
through ascending fibers to the nucleus posthabenularis from both
these nuclei, and descending fibers from it to the nucleus parvocellularis posterior ffig. 140, tr. preopt. posthah., j)ars ant. and pars
post, and tr. posthab. preopt., pars ant.).
OLFACTORY CENTERS IN TELEOSTS 231
There are also ascending and descending unmedullated fibers
running between the nucleus posthabenularis and the nucleus
intermedins {tr. intermed. posthab. and tr. posthab. intermed.).
Connections between the nucleus entopeduncularis and the
nucleus intermedins may likewise be found (tr. intermed. entoved.
and entoped. intermed.).
All of these latter short connections contain few fibers and in
many cases form little more than a reticular network between
different parts of closely related regions; they can not be demonstrated by means of Weigert preparations, but come out only
in the silver methods, particularly the Ram6n y Cajal. They are
chiefly important in emphasizing the intimate relation between
all parts of the brain, and particularly, closely related morphological areas, through the formatio reticularis.
This covers all of the direct olfactory connections which could
be identified, but does not include the further connections of the
different tertiary thalamic centers with other points in the diencephalon, mesencephalon, cerebellum, medulla and spinal cord.
Some of these are shown, however, in the Weigert transections.
It is expected that an article will appear later in which the morphological relations and functions of the different diencephalic
centers will be taken up in detail, in which these further connections will be brought out. Until that time, it is not deemed wise
to discuss in detail the morphological bearing of the thalamic
olfactory connections, although some points will be taken up
later in the interpretation of results.
5. THE CONDUCTION PATHWAYS
At this point it may be well to point out the different pathways
which an impulse of a given character may follow. Of the various possible, anatomically demonstrated paths open to a given
impulse, the one chosen under given conditions can be unquestionably accepted only when physiological evidence can be offered
in support. Nevertheless, impulses must follow conduction paths,
and we may, therefore, plot out anatomically extensive impulse
pathways with an exceptional degree of accuracy, as is shown in
the cases where a physiological check has been used.
232 RALPH EDWARD SHELDON
Descending pathways
Nervus terriiinalis. In this case an impulse may travel from
the periphery to ganglion cells situated among the olfactory nerve
fibers and thence to a decussation among the rostral cells of the
bed of the anterior commissure. Its further course is not known.
The olfactory neurones of the first order end throughout the
lateral, rostral and rostro-medial face of the bulb. Fibers from
all three areas form the tractus olfactorii lateralis, and medialis,
pars lateralis, for the nucleus olfactorius lateralis and nucleus
pyriformis of the basal lobes (fig. 137). From the lobus pyriformis originate the tractus teniae for the habenula of the opposite
side, and the tractus olfacto-hypothalamicus lateralis for the
nucleus cerebellaris hypothalami and the nucleus diffusus lobi
lateralis of the same side (fig. 137).
The corpus precommissurale stands in relation, chiefly, with
the more medial portion of the bulb, through the tractus olfactorius, pars medialis and pars lateralis, which terminate largely in
the nucleus medianus of the same and opposite side, in the commissure bed, and in the pars supracommissuralis of the same side.
The pars lateralis, after decussation, sends also a few fibers to the
nucleus intermedius (fig. 137).
From the corpus precommissurale there are, likewise, two great
pathways open. In one case cells with short neurites, forming
the fibrae preconmiissurales striatici, transfer the impulse to
the palaeostriatum, whence it is carried by the tractus striothalamicus to the nuclei anterior tuberis, prerotundus, rotundus,
subrotundus, posterior thalami, cerebellaris hypothalami and diffusus lobi lateralis of the same side; and the nuclei rotundus,
subrotundus, aud diffusus lobi lateralis of the opposite side (fig.
139). The other connection is through the median forebrain
bundle, which places the nucleus supracommissuralis chiefly,
but other parts of the corpus precommissurale as well, in relation
with the nuclei rotundus, subrotundus and posterior thalami.
A third connection, less prominent but of considerable morphological importaiice, is with the nucleus prcopticus. This receives
two small bundles from the nucleus medianus, the tractus mediano
OLFACTORY CENTERS IN TELEOSTS 233
preoptici and also secondary olfactory fibers from the tractus
olfactorius medialis, pars lateralis, before its decussation (fig. 136).
It thus receives both secondary and tertiary olfactory fibers.
Very similar to the precommissural, and of great morphological
significance, are the descending connections of the primordium
hippocampi. The latter receives secondary olfactory fibers from
the tractus olfactorius medialis, pars medialis, and gives rise to
fibers for the tractus olfacto-thalamicus, pars dorsalis, for the
diencephalon.
The important descending pathway from the nucleus preoptions is the tractus praethalamo-cinereus from the nucleus magnocellularis to the hypophysis, together with the nuclei lateralis and
ventralis tuberis. Besides this there is the tractus preopticotuberis from the same nucleus to the region of the nucleus posterior tuberis and the nucleus posthabenularis. Both of these
are probably neurones of the fourth order.
Important neurones, chiefly of the third order, connect the
nucleus preoptions with the habenulae, originating from all parts
of the nucleus (figs. 141, 142).
Neurones of the fourth order originate in the habenular ganglia
and pass caudo-ventrad, the fasciculus retroflexus for the corpus
interpedunculare, and the tractus habenulo-diencephalicus for the
formatio reticularis in the region of the nucleus posterior tuberis
(figs. 141, 142).
It will be noted, then, that the olfactory neurones of the first
order, or olfactory nerve, carries impulses to all parts of the lateral,
rostral and mesal aspects of the bulb. From the lateral part of the
bulb, chiefly, but also from the mesal, impulses are carried by
neurones of the second order to the lateral area of the basal lobes.
Thence neurones of the third order carry the impulse either to the
habenula, or else to the nucleus posterior thalami, or the diffuse
cellular area of the caudal part of the inferior lobes. From the
mesal portion of the bulb impulses are carried to all parts of the
mesal olfactory area, or corpus precommissurale and primordium
hippocampi, by neurones of the second order, which also reach the
nucleus preoptions, further caudally. From the mesal area impulses may travel by neurones of the third order to the palaeostria
234 RALPH EDWARD SHELDON
turn, and thence by quaternary fibers of the tractus strio-thalamicus to practically all the nuclei of the thalamus and hypothalamus.
Or impulses will more usually take a tract of the third order,
the median forebrain bundle, for the region of the nuclei rotundus,
subrotundus, posterior thalami. Other impulses may continue
into the nucleus preoptions with fibers of the third order, the
tractus mediano-preoptici, or may reach the more rostral parts of
the nucleus by means of fibers of the second order. Neurones of
the third order, largely, carry impulses from all parts of the
nucleus preoptions to the habenular ganglia. It is, therefore,
probable that the nucleus preoptions stands in much the same relation to the habenulae as does the nucleus pyriformis. From the
nucleus preoptions fibers of the fourth order reach the nucleus posterior tuberis and hypophysis, while from the habenulae such fibers
pass to the corpus interpedunculare and the medial thalamus.
Motor correlation probably takes place through two connections;
one of these isbyjneans of the corpus interpedunculare, which sends
fibers, according to Ram6n y Cajal and Edinger, to the nucleus
dorsalis tegmenti in higher forms, from which fibers undoubtedly
pass into the great bulbar and spinal descending tracts for the
transmission of somatic motor impulses. Other connections may
also develop when this nucleus and its relations are more thoroughly worked out. Another connection is by way of the tractus
thalamo-bulbares et spinales from the thalamus to the medulla
and cord (Johnston, '06). In teleosts the more usual motor
pathway for the simple direct olfactory impulses is probably by
way of the corpus interpedunculare. This pathway is the more
definitely laid down and involves the more direct connections.
An impulse may pass to any part of the bulb, practically, from
the olfactory mucous membrane, thence to the lateral olfactory
area, thence by the definite, medullated tractus teniae to the
habenular ganglia, thence by the powerful fasciculus retroflexus
to the corpus interpedunculare and thence to the tegmental region
of the mesencephalon, whence it may come into relation with the
motor areas of the midbrain, medulla and spinal cord.
The olfactory connection with the thalamus is not so simple
and direct. An impulse must pass from the corpus preconnnis
OLFACTORY CENTERS IN TELEOSTS 235
surale by way of the comparatively few fibrae precommissurales '
striatic! to the palaeostriatum and thence through the tractus
strio-thalamicus, or else from the corpus precommissurale by
way of the descending fibers of the medial forebrain bundle. In
neither of these cases do we find so definite and compact a pathway as that first outlined, wherefore we may conclude that the
first is the more usual path for the direct olfacto-motor reflexes.
Another possible motor connection is through the preopticohabenularis fibers to the habenular region, and thence through the
fasciculus retroflexus, as above indicated. This is probably a
very unusual pathway as the connections just mentio'ned are
very diffuse and are undoubtedly simply the vestiges of a once
powerful pathway, now of less functional importance (cf. Acipenser). The functions of these latter pathways will be considered
later.
It is quite probable that there exist also somatic fibers connecting the epithalamic with the visual centers, although such were not
demonstrated (Herrick, '10b, pp. 468-469). The relation between
the ventral hypothalamic region and the visceral (gustatory)
pathways in teleostean fishes will be brought out later (see also
the discussion in the above mentioned paper of Herrick) .
Ascending pathways
There is no evidence for the existence of centrifugal fibers in
the olfactory nerve bundles. Ascending fibers from the diencephalon include fibers from the lateral and ventral portions of the
inferior lobes to the nucleus pyriformis (tractus hypothalamoolfactorius lateralis) ; fibers from the ventro-lateral part of the
inferior lobes, the nucleus prerotundus and nucleus anterior
tuberis especially, and possibly the nucleus rotundus to the palaeostriatum and nucleus olfactorius lateralis by way of the tractus
thalamo-striaticus ; and the fibers from the nucleus posterior
tuberis to the corpus precommissurale. From the corpus precommissurale, nucleus medianus, fibers pass to the nucleus olfactorius anterior in the tractus olfactorius ascendens (figs. 136, 137).
236 RALPH EDWARD SHELDON
C. Judson Herrick traces the gustatory fibers of the fourth
order into the caudal portion of the inferior lobes; it is likewise
probable that tactile and other general sensory fibers reach the
dorsal thalamic region through the medial lemniscus fibers. It
is, therefore, probable, as Johnston and Herrick have already
pointed out, that the ascending fibers from the pars dorsalis of
the thalamus and from the hypothalamus are in the nature of
general somatic and visceral sensory forebrain connections, respectively. The relations of the nucleus posterior tuberis need to be
better understood, however, before the function of this ascending
tract can be stated positively. It may be a connection for the
transmission of visceral and somatic sensory impulses to the olfactory bulbs through the tractus olfactorius ascendens.
Association connections
Cajal and Golgi preparations show that practically all parts of
the brain are permeated by a closely meshed reticulum of fine
fibers, the 'Punktsubstanz' or formatio reticularis. In certain
preparations it is almost impossible to identify individual cells,
so close is the fibrous mesh. All parts of closely related regions,
such as the different nuclei of the corpus precommissurale, are
also placed in relation by means of large numbers of short connections. The same holds true with respect to regions derived
from, the same morphological structure. This explains the connections between the nucleus intermedins and the nucleus posthabenularis, both of which are probably parts of the same dorsal
olfactory column. It was noted earlier how the nucleus medianus
separates into dorsal and ventral columns; how the dorsal continues
caudo-laterad as the nucleus supracommissuralis, nucleus intermedins, nucleus posthabenularis and habenulae; and how the
ventral continues as the pars commissuralis, nucleus medianus
and the nucleus preopticus. It is, therefore, to be expected, after
what has been said regarding the close connection of associated
regions that these two dorsal and ventral columns would possess
short association connections. Such is the case and, while these
fibers have been given the name of tracts, they are really all a
OLFACTORY CENTERS IN TELEOSTS 237
part of the same set of association fibers. The connections include
all the nucleus preopticus-nucleus intermedius, posthabenularis,
ganglia habenularum, nucleus commissuralis, nucleus entopeduncularis connections (fig. 140) . Such connections also exist between
the corpus precommissurale and the primordium hippocampi.
Commissural connections ■
These include the commissura interbulbaris between the two
olfactory bulbs (?); the commissura hippocampi, pars anterior
connecting the two primordia hippocampi or nuclei dorsales;
the commissura hippocampi, pars posterior, joining the lobi pyriformes; the commissura corporium precommissuralium, between
the partes supracommissurales ; and the commissurae nucleorum
preopticorum, all present in the anterior commissure. The pyriform lobes may also be connected through the superior or habenular commissure forming a commissura aberrans.
The fonnatio reticularis
In any discussion of the different pathways it must never be
forgotten that the fine, reticular network of the formatio reticularis type is of great functional importance. In the past the
tendency has been to consider only the tracts laid down in definite
bundles. It is probable that in the phylogeny of a fiber tract the
heavily myelinated bundle is the latest stage. In early stages,
different areas are connected by a diffuse network of unmedullated fibers, through which impulses may take many courses. As
phylogenetic development proceeds, impulses tend to take more
and more definite paths through the maze of the reticulum;
thus the diffuse unmeduUated fiber connection is formed. Next
this diffuse connection becomes more compact and usually myelinated. It should not be implied that the myelinated tract is more
efficient for all connections, as it probably comes into existence
chiefly when there is necessity for a stereotyped reflex; to prevent,
possibly, 'loss of current' through diffusion, to use an electrical
analogy. In spite of this, there is no question but that the more
diffuse connections are of the utmost importance in putting into
238 RALPH EDWARD SHELDON
relation different parts of the nervous system, and in causing it to
react as one correlated, organic whole.
6. THE MORPHOLOGICAL AREAS OF THE FOREBRAIN
On the basis of the facts brought forward in the previous
discussion, the forebrain of teleosts may be divided into morphologically distinct centers, according to the following table:
Telencephalon.
Bulbus olfactorius
Nucleus olfactorius anterior
Pars lateralis hemisphaerii (pars dorso-lateralis, Herrick)
Nucleus olfactorius lateralis
Tuberculum anterius
Tuberculum laterale
Lobus pyriformis
Nucleus teniae
Pars medialis hemisphaerii (pars ventro-medialis, Herrick)
Corpus precommissurale
Nucleus medianus
Pars commissuralis
Pars supracommissuralis
(Nucleus intermedins, in part, at least) ,
Primordium hippocampi, or nucleus olfactorius dorsalis (pars dorso-medi
alis, Herrick)
Palaeostriatum (pars ventro-lateralis, Herrick)
Nucleus commissuralis lateralis
Nucleus entopeduncularis
Nucleus preopticus
Pars parvocellularis
Pars magnocollularis
Johnston ('11 j has made an important contribution to the morphology of th(^ forebrain of fishes in his analysis of the 'somatic
area' of selachians. This paper came into my hands after the
present contribution was ready for the press, and I have not had
an opportunity to make a thorough inquiry into the teleostean
homologies of this selachian area. Pending further study of
this question, I may say that it now seems probable that som(>
or all of the following regions of the carp brain correspond with
the selachian somatic area of Johnston: palaeostriatum, nucleus
teniae, nucleus intermedius of the precommissural body, nucleus
OLFACTORY CENTERS IN TELEOSTS 239
commissuralis lateralis and nucleus entopeduncularis. The fiber
connections of several of these nuclei are still very imperfectly
known and their morphological interpretation should therefore
be considered purely provisional until this knowledge is extended. ^
III. DISCUSSION
The structural plan of the teleostean diencephalon and telencephalon is very different from that of any other vertebrate type
excepting the higher ganoids (notably Amia); but as we follow
down the phylogenetic series through the lower ganoids to the
generalized fishes, we approach progressively nearer to the common vertebrate type. When the development of the teleostean
brain is more fully known it will probably prove easy to follow
here also the sequence of form changes from a generalized type.
It is generally accepted that the primitive form of the vertebrate central nervous system was a simple epithelial tube and that
from its rostral end two pairs of lateral vesicles were evaginated.
One of these comes from the diencephalon to form the optic vesicles: the other comes from the telencephalon to form the cerebral hemispheres. The telencephalon must be defined, as taught
by His and Johnston, as the rostral segment of the neural tube,
including the hemispheres evaginated from it, and not as the hemisperes alone, as in the BNA tables.
There is the greatest diversity in different vertebrate types
in the relative amounts of the telencephalic segment which are
evaginated into the hemispheres, but in no case is the whole of
this segment represented in the hemispheres. Accordingly,
we subdivide the telencephalon into telencephalon medium and
' Johnston's still more recent paper on the telencephalon of ganoids and teleosts (Jour. Comp. Neur., vol. 21, no. 6, December, 1911), appeared while this contribution was in press. His results differ in some matters of fact and in several
matters of interpretation from my own. So far as these concern the somatic or
non-olfactory connections, they do not fall within the scope of this article. Some
of his morphological conclusions 1 think rest upon an incomplete knowledge of
the anatomical facts; but since the homologies of the telencephalic and diencephalic centers in the carp and other lower vertebrates will be fully discussed in a
forthcoming paper, Johnston's conclusions will not be further considered at this
time.
240 RALPH EDWAKD SHELDON
cerebral hemispheres, and recognize that in general the hemispheres increase at the expense of the telencephalon medium as we
ascend the phylogenetic series. For further discussion of this
question, see Johnston ('09) and Herrick ('10 b). The latter
author, on the basis of the examination of a series of embryonic
and adult brains of different vertebrates, has studied the method
of evagination of the cerebral hemispheres in relation with the
functional connections of the different parts of the neural tube
involved in this process and has devised a schematic picture of
the probable relations of the functional subdivisions of the neural
tube in a primordial vertebrate whose optic and cerebral vesicles
were still in the unevaginated condition ('10 b, fig. 72). See
also Johnston ('11), fig. 82.
In such an ancestral type the sulcus limitans, terminating in the
preoptic recess, separates the ventral lamina of the neural tube
(Bodenplatte or hypencephalic region of His) from the dorsal
lamina (Fliigelplatte o-r epencephalic region) . The ventral lamina
therefore, ends in the chiasma ridge and all of the diencephalon
and telencephalon dorsal and rostral to the sulcus limitans belongs in the primary dorsal lamina, i.e., to the sensory or receptive region. The chief sensory function of this region was, in the
telencephalon, primitively, olfaction. The tissue in the ventral
part of this region, which lies in contact with the ventral (efferent) lamina behind, secondarily assumed the function of motor
correlation tissue, this part being usually above fishes separated
from the dorsal part by a sulcus, the sulcus medius (sulcus Monro! of authors), which in higher forms extends caudad from the
interventricular foramen. By a process of further differentiation the part above the sulcus medius becomes divided into epithalamus and pars dorsalis thalami, and the part below the sulcus
medius into pars ventralis thalami and hypothalamus, the latter
extending forward beyond the chiasma ridge into direct continuity with the preoptic nucleus.
The relations just described are preserved in the diencephalon
of adult brains of many of the Ichthyopsida and are visible
in embryos of many higher vertebrates. A transection taken
through the rostral end of the diencephalon, accordingly, in these
OLFACTORY CENTERS IN TELEOSTS 241
lower vertebrates shows, in addition to the membranous median
plates in the roof and floor, four longitudinal columns or laminae
on each side, viz., the epithalamus, pars dorsalis thalami, pars
ventralis thalami and hypothalamus (fig. 128). The last two
contain motor correlation tissue, with somatic and visceral elements, respectively, predominating.
In the primordial vertebrate these four columns proba'bly
extended forward into the telencephalon without fundamental
change. In all existing vertebrate types variable amounts of this
telencephalic tissue are evaginated to form the cerebral hemispheres. The olfactory bulb clearly formed the initial center of
evagination. In cyclostomes the hemisphere is composed of
olfactory bulb, with part of the secondary olfactory nucleus (these
coming from the telencephalic extension of the pars dorsalis
thalami), and a very small corpus striatum, this being an extension
of the pars ventralis thalami. In the lower elasmobranchs the
olfactory bulb is fully evaginated and the telencephalon medium
greatly elongated, with great thickening and a very slight evagination of its rostral end. In the higher sharks the telencephalon
medium is shortened in correlation with an increase in the thickening of the tissue about the lamina terminalis and the further evagination in this region of the secondary olfactory centers.
The Dipnoi show a very different line of specialization. The
olfactory bulbs are in all cases fully evaginated. The telencephalon is not greatly elongated (except in adult Ceratodus) and
its lateral walls are uniformly thickened and more or less completely evaginated to form the cerebral hemispheres, whose form
and structure, especially in the case of Lepidosiren, are very close
to those of Amphibia.
The morphology of the amphibian cerebral hemisphere has
been fully discussed in the paper cited (Herrick, '10 b), the author
showing that it is naturally divided into four parts (exclusive of
the olfactory bulb), viz., (1) pars dorso-medialis (primordium
hippocampi), (2) pars dorso-lateralis (primordium of the pyriform lobe), (3) pars ventro-lateralis (primordium of the corpus
striatum) and (4) pars ventro-medialis (precommissural body and
septum) . He shows further that these four parts are the telen
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3
242 RALPH EDWARD SHELDON
cephalic extensions respectively of (1) the epithalamus, (2) the pars
dorsalis thalami, (3) the pars ventralis thalami and (4) the hypothalamus and tissues surrounding the preoptic recess. The cerebral hemispheres of amniote vertebrates are modifications of this
fundamental pattern.
The teleostean forebrain conforms neither to the selachian nor
to the dipnoan and amphibian type. Further analysis of the series
of ganoidean types and of the ontogeny of the teleosts will doubtless shed light upon the steps by which the teleostean pecularities
have been acquired. The study of the form and fiber connections
of the adult brain, together with the available data bearing on
its phylogeny and ontogeny, suggests the following interpretation.
It is evident that the teleostean olfactory bulbs are completely
evaginated and that they have carried out with them a small
amount of secondary olfactory tissue, the nucleus olfactorius anterior. The remainder of the telencephalon remains unevaginated
as the telencephalon medium, which is, moreover, considerably
elongated. The failure of any considerable part of the telencephalon, except the olfactory bulbs, to evaginate laterally is the
basis of its difference from that of the Dipnoi and Amphibia.
The fact that the increase in its tissue takes place uniformly
throughout its length or somewhat more at its caudal end instead
of at its rostral end is the basis of its difference from the elasmobranchs.
The increase in the mass of the telencephalon occurs under
the influence of two chief factors: (1) olfactory impulses coming
in by way of the olfactory bulbs, (2) non-olfactory sensory impulses coming in for correlation purposes from the thalamus and
hypothalamus. The correlation sought in the lower forms was
exclusively with the olfactory apparatus; olfacto-somatic in the
case of the thalamic tracts, and olfacto-visceral in the case of the
hypothalamic tracts. In higher vertebrates the non-olfactory
systems effect correlations inter-se thus giving rise to the neopallium; but little, if any of this sort of correlation occurs in fishes.
In the teleostean brain, as has been pointed out earlier, the
arrangement of the telo-diencephalic centers in the form of
longitudinal columns, is plainly evident. At the rostral end of
OLFACTORY CENTERS IN TELEOSTS 243
the basal lobe the ventro-medial column appears in its primitive
relations, forming here the nucleus medianus of the precommissural body. Passing caudad the nucleus medianus bifurcates
at the anterior commissure into the dorsal pars supracommissuralis and the ventral pars commissuralis or commissure bed.
The latter is directly continuous with the nucleus preopticus,
which in turn grades almost insensibly into the hypothalamic
nuclei. The pars supracommissuralis becomes continuous caudally with the nucleus intermedins. The cells of the latter nucleus
likewise grade over into those of the nucleus posthabenularis and
habenula, but this connection is probably secondary, as will be
brought out later.
The other diencephalic columns are interrupted at the level
of the velum transversum save for the fiber tracts of the basal
forebrain bundles. Dorsal to the ventro-medial column lies the
primordium hippocampi rostrally, immediately above the corpus
precommissurale. This, the dorso-medial column of Herrick, is
probably the telencephalic extension of the epithalamic habenula
and nucleus posthabenularis of the diencephalon.
The nucleus entopeduncularis probably belongs to the same
column as the pars ventralis thalami, the pars ventro- lateralis
of Herrick, which expands rostrally to form the paleostriatum .
In the evaginated hemispheres of the Dipnoi and Amphibia the
striatal complex is carried outward into the ventro-lateral wall
of the hemisphere vesicle. In teleosts the wall as a whole does
not evaginate in this way; but the striatum complex, with the
associated lateral forebrain tract, moves outward within the
solid basal lobe away from the ventricular surface and toward the
lateral surface of the brain, a movement which has been carried
to a greater extreme in the 'somatic area' of elasmobranchs
(Johnston, '11). The precommissural body and the palaeostriatum are to be regarded as extensions of the hypothalamus and ventral part of the thalamus respectively and, therefore, as equivalent to the pars basalis, or pars subpallialis, of the amphibian
hemisphere. The remainder of the basal lobe is the extension
of the epithalamus and dorsal part of the thalamus and, therefore, is the equivalent of the pars pallialis of the amphibian brain.
244 RALPH EDWARD SHELDON
The olfactory crus is attached to the rostral end of the basal
lobe by two systems of tracts, a medial and a lateral. The former,
as in Amphibia, connects chiefly with the precommissural body
(tractus olfactorius medialis) and in smaller measure with
the dorso-medial part of the basal lobes termed primordium
hippocampi in this paper, this relation being in principle similar
to that of Amphibia and higher forms. The closely associated
nervus terminalis and tractus olfactorius ascendens have been
discussed in another connection. The tractus olfactorius lateralis
connects chiefly with the lateral part of the basal lobe, the
nucleus olfactorius lateralis and the nucleus pyriformis. These
nuclei correspond in a general way with the dorso-lateral part of the
amphibian hemisphere, or primordium of the lobus pyriformis.
Like the palaeostriatum, they tend to move laterad away from the
ventricular and toward the lateral surface of the basal lobe.
In vertebrates with evaginated hemipheres the two dorsal
parts (pars pallialis) lie on opposite sides of the lateral ventricle
and in later phylogenetic stages become respectively the hippocampus and the pyriform lobe. In the teleosts these parts are
very imperfectly separated, especially at the rostral end of the
basal lobe; here both are parts of a common secondary olfactory
nucleus. Incident to the progressive enlargement of the telencephalon without the evagination of its walls, the thickened secondary olfactory nucleus moves laterad, carrying with it the taenia,
or Une of attachment of the membranous roof, which accordingly becomes dilated laterally. (See figs. 126 to 134 illustrating
the arrangement of these parts and the process of eversion.)
It will be observed that the teleostean form has not been
reached by a simple process of eversion of the whole wall such as
that suggested by Mrs. Gage ('92; see fig. 135); for that would
bring the primordium hippocampi, which borders the taenia in
Amphibia, far ventro-laterally in the teleosts. This appears not
to be the case, but a portion of the dorsal secondary olfactory
nucleus retains its dorso-medial position with reference to the
other massive structures, in spite of the lateral movement of the
taenia. The movement in question is not, in fact, a simple lateral
bending of the whole wall at the sulcus limitans telencephali,
OLFACTORY CENTERS IN TELEOSTS 245
but rather a gradual plastic movement of the material, such that,
while the precommissural body and the medial part of the dorsal
olfactory nuclei remain in the original position, the intervening
portions of the lateral wall move toward the lateral part, thus
bringing the dorsal olfactory nucleus and the precommissural
body into contact at the sulcus limitans. The paleostriatum
moves laterad only a short distance, coming to occupy the middle
of the basal lobe. But a portion of the dorsal olfactory nucleus
and the whole of the lateral nucleus move to the extreme ventrolateral margin, carrying the taenia with them, thus forming at the
rostral end of the basal lobe the tuberculum laterale, and at the
caudal end the nucleus pyriformis.
The tuberculum anterius, tuberculum laterale, and nucleus
dorsalis are parts of the undifferentiated secondary olfactory
nucleus. The precommissural body and pyriform nucleus are
more highly differentiated parts of the secondary olfactory nucleus which have developed under the influence of ascending fibers
of the medial and lateral forebrain tracts respectively. The
palaeostriatum has become an efferent correlation center relatively free from direct olfactory connections. It is interesting
to note that the termination of the lateral hypothalamic tract
caudally in the teleosts has brought about the development of the
nucleus pyriformis at that point, while in the selachians the more
rostral ending of this connection (tractus pallii) has induced the
formation of the nucleus olfactorius lateralis and primordium
hippocampi in a correspondingly different position.
The selachians exhibit a considerably more highly differentiated
condition of all of the forebrain centers than is found in the teleosts (cf. Johnston, '11). The selachian ascending tract from the
hypothalamus to the primordium hippocampi (tractus pallii),
in teleosts is probably represented in the tractus hypothalamoolfactorius lateralis, a condition which resembles that of amphibians (Herrick, '10, p. 444).
The nucleus olfactorius dorsalis or primordium hippocampi
receives some fibers from the tractus olfactorius medialis, and this
connection is probably the reason why this portion of the undifferentiated secondary olfactory nucleus retains its dorso-medial
246 RALPH EDWARD SHELDON
position during the lateral eversion of the remainder of this
nucleus. The adult configuration is such as to suggest that the
nucleus dorsalis is homologous with the amphibian primordium
hippocampi and the sulcus limitans telencephali with the fissura
limitans hippocampi of Herrick (fissura arcuata of Gaupp).
The latter homology is however, manifestly incomplete, for the
fissura limitans hippocampi is a total fissure involving the whole
wall of an evaginated hemisphere, while the teleostean sulcus
limitans is an ependymal groove within the ventricle of the telencephalon medium. The two sulci in question separate homologous parts of the brain and are as nearly homologous as the
topographic relations of these two types of telencephalon permit.
Some justification may be found for the homology of the
nucleus olfactorius dorsalis with the primordium hippocampi of
Amphibia, although the apparent resemblance in position is an
argument rather against it than for it. It must not be forgotten that the nucleus dorsalis occupies a dorso-median position
below the telencephalic ventricle, not above it, as in Amphibia.
•In the process of eversion, to which reference was made above, the
whole of the dorsal nucleus might be expected to follow the taenia
in its lateral movement. The fact that a part of this nucleus
retains its position at the dorso-medial border of the basal lobe
has been alread}^ explained as due to its connection with the tractus olfactorius dorso-medialis. This is a primary connection of
the primordium hippocampi; cf. fig. 125 with C. J. Herrick ('10 b),
figs. 72, 73, 83 and 84, the nucleus olfactorius dorsalis or primordium hippocampi of the teleost being the functional equivalent
of Herrick' s dorso-medial ridge in spite of its position far removed
from the taenia. Nevertheless, the nucleus dorsalis shows few
other resemblances with the primordium hippocampi. It has
not been shown to receive large numbers of olfactory fibers of the
third or higher orders; it sends very few fibers to the anterior
commissure complex to form a commissura hippocampi and no
clearly defined columna fornicis fibers appear to arise from it,
though possibly the medial forebrain bundle may contain fil)crs
of this type.
OLFACTORY CENTERS IN TELEOSTS 247
It is concluded, therefore, that the materials found in the amphibian primordium hippocampi are not completely separated in
the teleosts from the other elements of the secondary olfactory
nucleus, being represented chiefly in the nucleus olfactorius dorsalis or primordium hippocampi and to a less degree perhaps in
the nucleus olfactorius lateralis and nucleus pyriformis.
The term 'epistriatum' has not been used in this article in the
description of the telencephalic nuclei, owing to the fact that it
has been applied by different authors, with resulting confusion,
to morphologically different structures. It was originally used
by Edinger ('96), to designate a structure found dorsal to the striatum in the lateral wall of the reptilian forebrain. Its connections
here show clearly that it is morphologically a lateral structure,
corresponding to the nucleus sphaericus of students of reptiles.
The epistriatum of birds, as described by Edinger, is likewise a
lateral structure. Turning to the so-called epistriatum of the
anamniotes, a different condition is immediately noted. Edinger
('06a) and Kappers ('06) describes as epistriatum in teleosts a
medial area reached by the tractus olfactorius medialis which
seems to include a part of our precommissural body, but in their
later works this name is applied to our nucleus olfactorius dorsalis. Catois uses the term for the dorsal portion of the
palaeostriatum. Johnston ('06) places the epistriatum of teleosts
on both the medial and lateral parts of each basal lobe, although
these two areas belong to morphologically different structures. It
is difficult to see how the term can continue in use without constantly increasing confusion. Even if all workers had clearly in
mind the morphological characteristics of the different varieties
of epistriatum, it would seem unwise to use the same name, even
with a modifying adjective, as does Kappers in his later work,
for such morphologically different structures.
From the preceding discussion it is clear that the localization of
function in the telencephalon of teleosts has not advanced so far
as in Amphibia and Dipnoi with more fully evaginated hemispheres. This is probably the explanation of the fact that the
diencephalic regions are also far less clearly analyzed than in Amphibia, and that nearly all parts of the basal lobes seem to be
248 RALPH EDWARD SHELDON
connected with both hypothalamic and thalamic centers. But
the discussion of these relations can be taken up more profitably
after the connections of the diencephalic nuclei are more fully
analyzed and particularly, after their embryological development
has been studied.
Some comment should be made on the bearing which the data
given in this article make with respect to the morphology of the
forebrain tela. It is clear from the facts presented that the forebrain of the teleostean fishes contains primordial pallium and
also the primordium of all important morphological structures
found in the forebrain of higher vertebrates. The pallium of
Rabl-Riickhard, then, is not the morphological equivalent of any
portion of the wall of the forebrain of higher vertebrates but is
simply a tela, derived from the Deckplatte of His. In fact there
is no evidence anywhere in the phylogeny of the vertebrate brain
that the Deckplatte gives rise to a nervous structure. The evidence which has been offered, then, gives additional support to
the views of Studnicka, already accepted by Kappers, Johnston,
Edinger and Herrick.
Anatomical Laboratories,
The School of Medicine,
University of Pittsburgh.
LITERATURE CITED
All papers cited have been consulted, excepting those marked with an asterisk
(*). The subject matter of articles so indicated was ascertained through reviews.
AiCHEL, Otto 1895 Kurze Mittheilung uber den histologischen Bau der lleichschleimhaut embryonalcr Teleostier. Sitzungsber. d. Gesellsch. f.
Morphol. u. Physiol, i. Munchen, Bd. 11, Hft. 2 u. 3, pp. 73-78.
Belloxci, Giuseppe 1880 Ricerche comparative suUa struttura dei centri
nervosi dei Vertebrati. Mem. d. r. Accad. d. Lincei, CI. sc. F., ser.
3, vol. 5, pp. 157-182, figs. 1-58.
1885 Intorno all' apparato olfattivo-ottico (nuclei rotondi, Fritsch)
del cervello dei Teleostei. Ibid., ser. 4, vol. 1, pp. 318-323, pi. 1.
Brookover, Charles. 1908 Pinkus's nerve in Amia and Lepidosteus. Science,
N.S., vol. 27, pp. 013-914.
1910 The olfactory nerve, the nervus terminalis and the preoptic
sympathetic system in Amia calva, L. Jour. Comp. Neur., vol. 20, pp.
49-118, pis. 1, text figs. 32.
OLFACTORY CENTERS IN TELEOSTS 249
BtTRCKHARDT, R. 1892 Das Centralnervensystem von Protopterus annectens.
Eine vergleichend-anatomische Studie. Berlin, Friedlander u. Sohn,
Taf. 1-5, pp. 1-64.
Calleja C. *1893 La region olfatoria del cerebro en los urodelos. Madrid.
Catois, E. H. 1902 Recherches sur I'histologie et I'anatomie microscopique
de I'encephale chez les poissons. Bull, scientifique de la France et
de la Belgique. Tom. 36, pp. 1-166, pis. 1-10.
Edingbr, L. 1888 Untersuchungen liber die vergleichendeAnatomiedesGehirns.
I. Das Vorderhirn. Abhdlg. d. Senckenberg. Naturf. Gesellsch., Bd.
15, pp. 91-122, pis. 1-4.
1892 Untersuchungen liber die vergleichende Anatomie des Gehirns.
II. Das Zwischenhirn. Erster Teil. Das Zwischenhirn der Selachier
und der Amphibien. Ibid., Bd. 18, pp. 1-55, pis. 1-5, text fig. 1.
1893 Vergleichend-entwickelungsgeschichte und anatomische Studien
im Bereiche der Hirnanatomie. iii. Riechapparat und Ammonshorn.
Anat. Anz., Bd. 8, pp. 305-321, text figs. 6.
1894 Vergleichent-anatomische und entwickelungsgeschichtliche Studien im Bereiche der Hirnanatomie. iv. Die Faserung aus dem Stammganglion Corpus striatum. Vergl.-anat. u. exp. Untersucht. Verhandl.
der Anat Gesellsch., pp. 53-60, figs. 1-4.
1896 Untersuchungen liber die vergleichende Anatomie des Gehirns.
III. Neue Studien liber das Vorderhirn der Reptilien, Abhdlg. d. Senckenberg. Naturf. Gesellsch., Bd. 19, pp. 313-387, pis. 1-4, text figs. 14.
1896 a Vorlesungen liber den Bau der nervosen Zentralorgane. Auf. 5.
Leipzig.
1899 Untersuchungen liber die vergleichende Anatomie des Gehirns.
IV. Studien liber das Zwischenhirn der Reptilien. Ibid., Bd. 20, pp.
161-197, pis. 1-3.
1908 Vorlesungen liber den Bau der nervosen Zentralorgane des Menschen und der Tiere. Bd. 2, Auf. 7, pp. 12, 334, figs. 283. Leipzig.
Fritsch, G. 1878 Untersuchungen uber den feineren Bau des Fischgehirns.
Berlin pp. 1*5, 94, pis. 1-13.
Gage, Susanna Phelps 1893 The brain of Diemyctylus viridescens from larval
to adult life. Wilder Quarter Century Book, Ithaca, N. Y., pp. 259314, pis. 1-8.
Gaupp, Ernst 1899 A. Ecker's und R. Wiedersheim's Anatomie des Frosches.
Zw. Abth., Lehre vom Nerven- und Gefasssystem. Zw. Auf., Braunschweig, pp. 12, 548, figs. 146.
Goldstein, Kurt 1905 Untersuchungen liber das Vorderhirn und Zwischenhirn einiger Knochenfische. (Nebst einigen Beitragen liber Mittelhirn
und Kleinhirn derselben). Arch. f. mikr. Anat u. Entw., Bd. 66, pp.
135-219, pis. 11-15, text figs. 23.
250 RALPH EDWARD SHELDON
Haller, Bela 1898 Vom Bau des Wirbelthiergehirns. i Thiel. Salmo und
Scyllium. Morph. Jahrb., Bd. 26, pp. 345-641, pis. 12-22.
Hardesty, 1. 1902 Neurological technique, pp. 12, 183, Chicago.
Herrick, C. Judson 1897 Report upon a series of experiments with the Weigert methods, with special reference for use in lower brain morphology.
State Hospitals Bull., Utica, N. Y., vol. 2, pp. 1-31.
1909 The nervus terminalis (nerve of Pinkus) in the frog. Jour. Comp.
Neur., vol. 19, pp. 175-190, figs. 1-10.
1910 a The morphology of the cerebral hemispheres in Amphibia.
Anat. Anz., Bd. 36, pp. 645-652, figs. 1-3.
1910 b The morphology of the forebrain in Amphibia and Reptilia.
Jour. Comp. Neur., vol. 20, pp. 413-547, figs. 1-84.
Herrick, C. L. 1891 a The commissures and histology of the teleost brain.
Anat. Anz., Bd., 6 pp. 676-681, figs. 1-3.
1891 b Contributions to the comparative morphology of the central
nervous system, ii. Topography and histology of the brain of certain
reptiles. Jour. Comp. Neur., vol. 1, pp. 14-27, pis. 3, 4, 9.
1891 c Contributions to the morphology of the brains of bony fishes.
II. Studies on the brains of some American fresh-water fishes. A. Topography. Ibid., pp. 228-245, pis. 19-21.
1891 d Contributions to the morphology of the brains of bony fishes.
II. Studies on the brains of some American fresh-water fishes. (Continued.) B. Histology of the rhinencephalon and prosencephalon. Ibid.,
pp. 333-358, pis. 24-25.
1892 a Additional notes on the teleost brain. Anat. Anz., Bd. 7, pp.
422-431, figs. 1-10.
1892 b Contributions to the morphology of the brain of bony fishes.
II. Studies on the brain of some American fresh-water fishes. (Continued.) C. Histology of the diencephalon and mesencephalon. Jour.
Comp. Neur., vol. 2, pp. 21-72, pis. 4-12.
1892 c Notes upon the anatomy and histologj^ ,of the prosencephalon
of teleosts. Am. Nat., vol. 26, pp. 112-120, pis. 7-8.
Johnston, J. B. 1898 The olfactory lobes, fore-brain and habenular tracts of
Acipenser. Zool. Bull., vol. 1, pp. 221-241, figs. 1-5.
1901 The brain of Acipenser. Zool. Jahrb., Abth. f. Anat. u. Ont., pp.
59-260, pis. 2-13.
1902 The brain of Bctromyzon. Jo\ir. Comp. Neur., vol. 12, jjp. 1-86,
pis. 1-8.
1906 The nervous system of vertebrates. Pp. 20, 370, fig.s. 1-180,
Phihidelpliia.
OLFACTORY CENTERS IN TELEOSTS 251
Johnston, J. B. 1909 The morphology of the forebrain vesicle in vertebrates.
Jour. Comp. Neur., vol. 19, pp. 457-539, figs. 1-45.
1910 The evolution of the cerebral cortex. Anat. Rec, vol. 4, ))p.
143-166, figs. 1-20.
1911 The telencephalon of selachians. Jour. Comp. Neur., vol. 21,
pp. 1^114, figs. 1-85.
Kappers, C. U. Ariens 1906 The structure of the teleostean and selachian
brain. Jour. Comp. Neur., vol. 16, pp. 1-112, pis. 1-16.
1907 Untersuchungen iiber das Gehirn der Ganoiden Amia calva und
Lepidosteus osseus. Abhdlg. d. Senckenberg. Naturf. Gesellsch., Bd.
30., pp. 449-500, pi. 18, text figs. 1-6.
1908 a (Mirwirkung von W. F. Theunissen) Die Phylogenese des
Rhinencephalons, des Corpus striatum und der Vorderhirncommissuren.
Folia Neuro-Biologica, Bd. 1, pp. 173-288, pis. 1-3, text figs. 1-5.
1908 b Weitere Mittellungen iiber die Phylogenese des Corpus striatum und des Thalamus. Anat Anz., Bd. 33, pp. 321-336, figs. 1-6.
1908 c Eversion and inversion of the dorso-lateral wall in different
parts of the brain. Journ. Comp. Neur., vol. 18, pp. 433-436, figs. 1-5.
1909 The phylogenesis of the palaeo-cortexandarchi-cortex compared
with the evolution of the visual neo-cortex. Archives of Neurol, and
Psychiat., vol. 4, pp. 1-13, pis. 1-4.
Kappers, C. U. A., and Theunissen, W. F. 1907 Zurvergleichenden Anatomie
des Vorderhirns der Vertebraten. Anat. Anz., Bd. 30, pp. 496-509,
figs. 1-10.
KoELLiKER, A. 1896 Handbuch der Gewebelehre des Menschen. 6Auf., Zw.
Bd., Nervensystem des Menschen und der Thiere, pp. 8, 1-874, figs.
330-845. Leipzig.
LocY, W. A. 1899 New facts regarding the development of the olfactory nerve.
Anat. Anz., Bd. 16, pp. 273-290, figs. 1-14.
1903 A new cranial nerve in selachians. Mark Anniversary Vol., pp.
39-55, pis. 5-6.
1905 On a newly recognized nerve connected with the forebrain of
selachians. Anat. Anz., Bd. 26, pp. 33-63, 111-123.
Owen, Richard 1868 Anatomy of vertebrates, vol. 3, Mammals, jip. 10, 915,
figs. 1-614. London.
Rabl-Rxjckhard, H. 1882 Zur Deutung und Entwickelung des Gehirns der
Knochenfische. Arch. f. Anat. u. Physiol., Anat. Abth., pp. 111-138,
pis. 6-7.
1883 Das Grosshirn der Knochfische und seine Anhangsgebilde.
Ibid., pp. 279-322, pis. 12-13.
252 RALPH EDWARD SHELDON
R.\BL-RtJcKHARD, H. 1884 Das Gehirn d^s Knochenfische. Biol. Centralbl.,
Bd. 4, pp. 499-510, 528-541, figs. 1-11.
1893 Das VorderhiinderCranioten. Eine Antwort an F. K. Studnifika.
Anat. Anz., vol. 9, pp. 536-547, figs. 1-16.
1894 Noch ein Wort an Herrn Studnicka. Anat, Anz., Bd. 10, p. 240.
Ram6n, Pedro *1894 Investigaciones micrograficas en elenc6falode los Batraceos y Reptiles. Zaragoza.
1896 L'Encephale des amphibiens. Bibliographic anatomique, T.
4, pp. 232-252, figs. 1-15.
R.\m6n y Cajal, S. 1894 Notas preventivas sobre la estructura del encephalo
de los Teleosteos. Anal. d. 1. Soc. Esp. d. Hist. Nat., Madrid, ser. 2,
T. 13.
1899 Textura del sistema nervioso del hombre y de los vertebrados.
T. 1. pp. xi, 566, figs. 1-206. Madrid.
1904 Ibid., T. 2, pp. 1-1209, figs. 207-887. Madrid.
Rath, O. vom 1895 Zur Consirvirungstechnik. Anat. Anz., Bd. 11. pp. 280-288.
RuBASCHiN, W. 1903 tjber die Beziehungen des Nervus trigeminus zur Reichschleimhaut. Anat. Anz., Bd. 22, pp. 407-415, figs. 1-4.
Sheldon, R. E. 1908 a An analysis of the olfactory paths and centers in fishes.
Anat Rec, vol. 2, pp. 108-109.
1908 b The participation of meduUated fibers in the innervation of the
olfactory mucousmembrane of fishes. Science, N. S., vol. 27, pp. 915-916.
1909 a The nervus terminalis in the carp. Jour. Comp. Neur., vol. ]9,
pp. 191-201, figs. 1-7.
1909 b The reactions of the dogfish to chemical stimuli. Ibid., pp.
273-311, figs. 1-3.
Sheldon, R. E. and Brookover, Charles 1909 The nervus terminalis in
teleosts. Anat. Rec, vol. 3, pp. 257-259.
Smith, G. Elliot 1895 The connection between the olfactory bulb and the
hippocampus. Anat. Anz., Bd. 10, pp. 470-474, figs. 1-2.
1903 On the morphology of the cerebral commissures in the vertebrata,
with special reference to an aberrant commissure found in the forebrain of certain reptiles. Trans. Linn. Soc. London, 2d Ser. Zool.,
vol. 8, pt. 12, pp. 455-500, figs. 1-36.
1908 The cerebral cortex in Lepidosiren, with comparative notes on
the interpretation of certain features of the forebrain in other vertebrates. Anat. Anz., Bd. 33, pp. 513-540, figs. 1-18.
OLFACTORY CENTERS IN TELEOSTS 253
Sterzi, Giuseppe 1907 II sistema nervoso centrale dei vertebrati. Ricerche
anatomische ed embriologiche, vol. primo, Ciclostomi, pp. 731, figs.
194, Padova.
1909 Ibid., vol. 2, Pesci, Lib. 1, Selaci, Pt. 1, Anatomia. pp. 986, figs.
385. Padova.
Stieda, L. 1868 Studien iibei- das centrale Nervensystem der Knochenfische.
Zeit. f. wiss. Zool., Bd. 18, pp. 1-72, pis. 1-2.
1870 Studien iiber das centrale Nervensystem der Wirbelthiere. Zeit.
f. wiss. Zool., Bd. 20, pp. 1-184, pis. 17-20.
1873 tjber die Deutung der einzelnen Thiele des Fischgehirns. Zeit.
f. wiss. Zool., Bd. 23.
StudniCka, F. K. 1893 a Zur Losung einiger Fragen aus der Morphologie des
Voderhirnes der Cranioten. Vorlaufige Mitteilung. Anat. Anz., Bd.
9, pp. 307-320, pis. 2-3.
1893 b Eine Antwort auf die Bemerkungen R. Burckhardt's zu meiner
vorlaufigen Mittheilung iiber das Vorderhirn der Cranioten. Ibid.,
pp. 691-693.
1894 Zur Geshichte des 'Cortex cerebri.' Verb. d. Anat. Gesellsch.,
8. Vers. Strassburg, pp. 193-198, fig. 1.
1895 a Bemerkungen zu dem Aufsatze : ' Das Vorderhirn der Cranioten'
von Rabl-Ruckhard. Anat. Anz., Bd. 10, pp. 130-137.
1895 b Beitrage zur Anatomic und Entwickelungsgeschichte des Vorderhirns der Cranioten. Erste. Abth., Sitzungsber. d. Konigl. Bohm.
Gesellsch. d. Wissensch., math.-naturw. Klasse, pp. 1-42, pis. 1-7.
1896 Ibid., Zw. Abth. pp. 1-32, pis. 1-4.
1898 Noch einige Worte zu meinen Abhandlungen iiber die Anatomie
des Vorderhirns. Anat. Anz., Bd. 14, pp. 561-569.
Van Gehuchten, A. 1890 Contributions a 1' etude de la muqueuse olf active
chez les mammiferes. La cellule, T. 6, fasc. 2, pp. 395-409, pi. 1.
1894 Contribution a 1' etude du systeme nerveux des t61eosteens (communication preliminaire). Ibid., T. 10, pp. 253-296, pis. 1-3.
1906 Anatomie du systeme nerveux de I'homme. 4th Edit., pp. 15,
999, figs. 1-848. Louvain.
WiEDERSHEiM, Robert 1902 VergleichendeAnatomie der Wirbelthiere. 5 Auf ,
pp. 19, 686, figs. 379. Jena.
EXPLANATION OF FIGURES
All drawings are made from the brain of the carp, Cyprinus carpio L. The
individual specimens from which these are made range from 15 to 30 cm. in length
for the Golgi preparations; 25 to 40 cm. for those prepared with toluidin blue and
the method of Ramon y Cajal, and 35 to 60 cm. for the Weigert preparations.
Figs. 1 to 4 were drawn with the use of a dissecting microscope; for all others there
were used a camera lucida and Zeiss microscope with the following objective and
ocular combinations: compensating ocular 4*, objective A*; compensating ocular
8, objective A*; ocular 2, objective AA; ocular 4, objective AA; ocular 6, objective AA; compensating ocular 6, objective AA; compensating ocular 4, apochromatic objective 16 mm. ; compensating ocular 4*, apochromatic objective 8 mm.;
compensating ocular 18, apochromatic objective 4 mm.
On all figures from longitudinal sections an arrow (— >) is placed always pointing
rostrad. Where a double pointed arrow (< >) appears after the name of a tract
it signifies that the tract in question contains both ascending and descending fibers ;
the name used on the figures is, however, always that of the descending tract.
All figures from the Weigert or toluidin blue method are from transections; in
the case of the latter every cell appearing in the section is drawn in with a camera
lucida in order to obtain the proper grouping.
The eight diagrams, figs. 125, and 136 to 142, consist in each case of a basal diagram, the same in figs. 125 and 141, and in figs. 136 to 140, 142; to which is added in
one or more different colors, the fiber connections. The two different basal diagrams are made from series of adjacent sections by the Weigert method, sagittal
in the case of figs. 125 and 141, frontal in figs. 136 to 140, 142. These are drawn
with tjje aid of a camera lucida, a Zeiss comp. oc. 4*, and objective A*, and are
superimposed in such a way as to bring as many as possible of the structures to be
considered into one figure. The relations are not, of course, accurate for any one
given plane. The fiber tracts are represented by simple lines showing the course
of each tract and its connections. The tracts so represented, are not, of course,
equal in respect to number of fibers; some, such as the lateral forebrain bundle,
are composed of an enormous number, while others, such as the tr. preopticohabenularis, pars posterior, contain only a few.
255
PLATE 1
EXPLANATION OF FIGURE
1 Dorsal aspect of the brain of the carp. X 2.
a, dorsal-lateral protuberance on the surface of the olfactory bulb caused by the
entering fibers of the olfactory nerve ; bulb, olf., bulbus olf actorius ;cbl., cerebellum ;
crus olf., crus olfactorium ; gran^. bas., ganglion basale of the cerebral hemispheres ;
lob. fac, lobus facialis or tuberculumimpar; Zo&. vag., lobus vagi; mesotela, membranous roof of the mesencephalon; rhinotela, membranous roof of the cavity of
the olf actory crus, the rhinocele; sac. dors., saccus dorsalis, enclosing the corpus
pineale; sp. cord, spinal cord; tela., membranous roof of the fourth ventricle;
tectum, tectum mesencephali; torus long., torus longitudinalis; valvula, valvula
cerebelli, showing through the membranous mesotela.
250
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 1
bulb
257
KATHARINE HILL, DEL.
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3
PLATE 2
EXPLANATION OF FIGURES
2 Dorsal aspect of the rostral end of the brain. X 4. The optic lobes are
removed and the tela of the cerebral hemispheres, the so-called pallium, is torn
from the dorsal surface, exposing the basal ganglia.
3 Left lateral aspect of the rostral end of the brain. X 4. Optic lobes and
tela as in fig. 2.
crusolf., crus olfactorium; hyp., pars gl., hypophysis, pars glandularis; hyp.,
pars, nerv., hypophysis, pars nervosa; lob. inf., lobus inferior or hypoarium; A'.
///, nervus oculomotorius; n. opt., nervus opticus; n. cbl., protuberance caused by
the development of the nucleus cerebellaris hypothalami of Goldstein; n. prerot.
+ n. rot., protuberance caused by the development of the nucleus prerotundus
and nucleus rotundus centrally; s. ypsil., sulcus ypsiliformis of Goldstein,
the rostral prolongation of which corresponds morphologically to the fovea
endorhinalis interna of Kappers and Theunissen ('08) ; tela, this indicates the torn
edge of the tela or pallium which covers the basal ganglia, extending rostrally
over the olfactory tracts to the olfactory bulbs, and caudally between the two
halves of the tectum, over the valvula; //•. olf. lat., tractus olfactorius lateralis, the
radix olfactoria lateralis of Kappers; tr. olf. med., tractus olfactorius medialis,
including also the tractus olfactorius ascendens and nervus terminalis; the corresponding tracts, according to Kappers are, tractus olfacto-lobaris medialis and
radix olfactoria medialis propria; he failed to note the nervus terminalis; tub. ant.,
tuberculum anterius; due chiefly, to the presence underneath, of the rostral end of
the nucleus olfactorius lateralis ; tub. dors., tuberculum dorsale, enlargement due
to the development of the nucleus olfactorius dorsalis; ^(/?). /«/., tuberculum laterale, caused by the development of the nucleus olfactorius lateralis; tub. post.,
tuberculum posterius, due to the development of the nucleus pyriformis.
258
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD .SHELDON
KATHARINE HILL, DEL.
259
PLATE 3
EXPLANATION OF FIGURES
4 Ventral aspect of the rostral end of the brain. X 4.
5 Transection through the median ridge of the olfactory mucosa to show its
innervation by trigeminal nerve fibers. Weigert method. X 64. In adjacent
sections the medullated fibers may be seen reaching the membrana propria. Note
that the epithelium of the median ridge differs from that of the remainder of the
Schneiderian membrane, particularly in the large number of goblet cells present.
This is also a characteristic of the respiratory epithelium of mammals as distinguished from the olfactory epithelium, which lacks almost entirely the mucus
secreting cells.
chias., optic chiasma; c. mam., corpus mammillare of Goldstein; fib. trig.,
fibrae trigemini;/. end., fissuraendorhinalis, the sulcus rhinalis of Kappers ('06),
the fovea endorhinalis externa of Kappers and Theunissen ('08), the fovea
limbica of Goldstein, the fissura ectorhinalis of Owen; go. cells., goblet cells;
hyji.. pnr.K gl., hypophysis, pars glandularis; hi/p.. pars iierv.. hypophysis, pars
nervosa; lam., lamella; lob. inf., lobus inferior; lob. lal., lobus lateralis hypothalami; lob. med., lobus medius hypothalami, of which the rostral part is the
tuber or tuber cinereum and the caudal the pars infundibularis; niemb. olf., membrana olfactoria, or olfactory portion of the Schneiderian membrane; mevih. resp.,
membrana respiratoria, the respiratory part of the Schneiderian membrane;
>n. opt., nervus opticus; sac. vase, saccus vasculosus; s. mam., sulcus manimillaris
of Goldstein, separating the region of the corpus mammillare from the remainder
of the lobus lateralis; tub. post., tuberculum posterius.
260
OLFACTORY CENTERS IX TELEOSTS
RALPH EDWARD SHELDOX
PLATE 3
c. rricrri
-lob. \nl
go. ceHs.
memb. -resp.
fib. trig,
memb. olf.
261
PLATE 4
EXPLANATION OF FIGURES
6 Transeclioii thiougli the iniddU' of the right olfactory bulb. Weigcrt method.
X 31. Most of the stippled periphery is filled with the unmedullated fibers of the
olfactory nerve which are ending in glomeruli in this region. An especially prominent mass of such fibers appears dorso-laterally, forming the ])rotuberance 'a,'
as shown in fig. 1.
7 (ianglion cell of the nervus terminalis. Golgi method. X 93. See fig. 124
for the position of this cell.
8 to 12 Mitral cells of the olfactory bulb. Golgi method. X 93. In the cells
from transverse sections an arrow points toward the center of the bulb ; in sagittal
or horizontal sections the arrow points diametrically away from the olfactory
crus and toward the center of the bulb. Figs. 8 and 9 are from transverse sections,
figs. 10 and 12 from longitudinal section of the bulb.
13 Fusiform cell from nucleus olfactorius anterior. Longitudinal section.
Golgi method. X 93. Arrow as in figs. 8 to 12. This neurone extends diagonally across the bulb, one end entering a glomerulus.
14 Stellate cell from nucleus olfactorius anterior. Transverse section. Golgi
method. X 93. Arrow as in figs. 8 to 12. Large numbers of these cells are found,
most of which are connected with glomeruli ; some of these glomeruli contain mitral
cell dendrites, while many are small and are, apparently, formed only by stellate
cell and olfactory nerve processes.
15 to 17 Neurones from the nucleus olfactorius anterior. Golgi luctliod.
X 93. Arrow placed as in figs. 8 to 12.
15 Stellate cell, connecting with a mitral cell glomerulus. From longitudinal
section.
16 Stellate cell from longitudinal section. Shows one dendrite in connect ion
with a glomerulus, while the neurite extends toward the center of the bull).
17 Fusiform cell from longitudinal section.
(lend., dendrite; //. /( rni.. nervus terminalis; ncur., ncui-ite; alf. nci-rc. olfactory
nerve, fibers of which are scattered about the perii)hery at the j)oints noted ; //■.
olf. Int., pars inlermed., tractus olfactorius lateralis, pars intermedia; tr. olJ.Uit.
parti. 7ned., tractus olfactorius lateralis, pars medial is ;/r. (ilf.med., par slat., tractus
olfactorius medialis, i)ars lateralis; Ir. olf. med., par.^. ti/ed., tractus olfactorius
medialis, j)ars medialis.
262
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 4
n.tcrin
263
PLATE 5
EXPLAXATIOX OF FIGURES
18 to 20 Neurones from the nucleus olfactorius anterior. Golgi method.
X 93. Arrow placed as in figs. 8 to 12.
18 Goblet shaped cell from longitudinal section.
19 Fusiform granule cell from longitudinal section.
20 Stellate granule cell from longitudinal section.
21 Fusiform cell from sagittal section of the olfactory bulb, showing neurite
entering the crus. Golgi method. X 93.
22 Tran,section through the middle of the right olfactory crus. Weigert
method. X 33. This section was drawn to show, particularly, the nervus terminalis; the remaining fiber pathways do not come out so clearly as in other series.
23 Transection through the caudal part of the right olfactory crus, innnediately
rostral to the cerebral hemispheres. Weigert method. X 33.
24 Transection through the rostral portion of the cerebral hemispheres. Weigert method. X 17. This section shows the relation to the hemispheres, of the
tracts of the crura.
bull), off., bulbus olfactorius; crus ulf., crus olfactorium; /. cndurh., fissura
endorhinalis; n. term., nervus terminalis; neur., neurite; tr. olf. asc, tractus
olfactorius ascendens, the radix olfactoria medialis i)ropria of Kappers; //■. olf.
nsc, jxirs Int., tractus olfactorius ascendens, pars lateralis; ir. olf. r/.sr., purs,
uied., tractus olfactorius ascendens, pars medialis; /;•. olf. lal., pars intermed.,
tractus olfactorius lateralis, pars intermediti; //■. olf. Int., jxirs Int., tractus
olfactorius lateralis, pars lateralis; tr. olf. hit., imrs. nied., tractus olfactorius
lateralis, pars medialis; //•. (df. ined., pars Int.. Iractus olfactorius medialis,
pars lateralis; tr. olf. med., pars mid., tractus olfactorius medialis, pars medialis.
264
OLFACTORY CEXTEHS IN TELEOSTS
RAI PH EDWARD SHEt.DOX
PLATE 5
trolf. med
pevrs med
tt: olf mec
n. term
tiro If. gvsc.
pars med.
trolf. 3sSC.
epithelial roof
tc olf. lat.
tt: olf. ]dt. p3^r5
inteftned.
trolf.Utpa^rsmed.
Xr olf a5c ^«, \?;
pa^fsmed .\- u
trolfasc ^ L*
pars med.^^- ■ &!g^^ / -W^| ^^-^p^tK olf lat
v*^ ^^^|r^ pa.f5 1 at
tr. olf med. ^ - ' l^ J " ^V>^r,^^4^tr olf laf pars
trolfla^t
pSkfs med
265
PLATE 6
EXPLANATION OF FIGURES
25 Transection through the rostral portion of the left cerebral hemisphere,
slightly caudal to fig. 24. Toluidin blue method. X 46.
26 Cells of the nucleus medianus. Toluidin blue method. X 575. From
transection. This nucleus is characterized by the arrangement of the cells in
small, closely packed groups as shown in the figure. Compare fig. 25.
27 Oblique longitudinal section through the hemispheres showing the origin
of the centrifugal fibers of the tractus olfactorius ascendens. Golgi method.
X 9. The section is much nearer the frontal than the sagittal plane, as is shown
by the inclusion of both olfactory crura, a portion of both optic nerves and much
of the anterior commissure.
emu. (int., commissura anterior; corp. pi-ccum., ii. nwd., corpus i)recommissurale, nucleus medianus, this latter is the rostral end of the group of cells called
'lobus olfactorius posterior, pars medialis' by Goldstein; ' area olfactoria posterior
medialis' and 'epistriatum' by Kappers ('06); 'area praecommissuralis septi'
by Kappers and Theunissen ('08); 'ganglion modiale septi' by Gaupp ('99) and
'paraterminal body' by Elliot Smith ('03); crura olf., cinira olfactoria;/. endorh.,
fissura endorhinalis; hyp., hypophysis: //. oj)l., nervus opticus; nucl. olf. dors.,
nucleus olfactorius dorsalis; iiucl. olf. lat.. nucleus olfactorius lateralis; palaeostr.,
palaeostriatum; .s. liin. lei., sulcus limitans telencephali; .s. ijpsil., fur. mil., sulcus
\'psiliformis, furca anterior, the fovea endorhiiuilis interna of Kappers; tr. olf.
asc, tractus olfactorius ascendens; //•. olf. inal., tractus olfactorius medialis.
2GG
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 6
v<4
p^:'::'f^'^ V.;(^^.'yrvV:'^^'V;rtv-<;. ^/^^j^^-^^:-. y^}^=-i^f^^
- '.jyp5ii.,fu-K ant.
liicl. o!f. dor3.
rura olf.
267
PLATE 7
EXPLANATION OF FIGURES
2.S-30 Cells of origin of the fibers of the tractus olfactorius ascendens. Golgi
method. X 93. These cells lie in the rostral portion of the precommissural body,
in the nucleus medianus (see fig. 27). They are taken from a sagittal series and
show the branching of the dendritos among the cells of the nucleus. The neurites
terminate in the nucleus olfactorius anterior of the olfactory bulb.
31 Association cell of the nucleus medianus. Golgi method. X 93. From
sagittal section.
32-33 Cells of the rostral part of the nucleus olfactorius lateralis. Golgi
method. X 93. The neurite of fig. 32 enters the tractus strio-thalamicus, while
that (if fig. 33 apparently ends in the vcntro-lateral portion of the hemisphere.
The cells are taken from a sagittal series and occupy a position about midway
between the dorsal and ventral surfaces of the hemisphere.
34 Transection through the cerebral hemispheres immediately rostral to the
anterior commissure. Weigert method. X 17. The nervus terminalis is, at this
level, separated from the tractus olfactorius medialis, preparatory to its decussation ; the two components of the tractus olfactorius medialis likewise appear distinctly.
cum. inlirhulh., commissura interbulbaris; /. e7td., fissura endorhinalis; n.
tenit.. nervus terminalis; .s. ijpsil., ant. h"w6, sulcus ypsiliformis, anterior limb;
Ir. o'f. Inl.. ti-actus olfactorius lateralis spreading in the form of a crescent to end
in the nucleus olfactorius lateralis, //•. olf. med., pan^ hil.. Iractus olfactorius medialis. pars lateralis; //•. olf. invd., pars mod., tractus olfactorius medialis, jiars medialis: //•. .slrio-lhdl.. t ractus si i-jo-thalamicus ; bum lies ap])earing here are made up,
inain!\'. of fibers wliidi do not decussate.
268
OLFACTORY CENTERS IN TELEOSTS
HAI.PH EDWARD SHELDON
T3
C
-0
28
34 "f
269
PLATE 8
EXPLANATION OF FIGUKES
35 Transrctiun through the hemispheres at the rostral margin of the anterior
commissure. Weigert method. X 17. This section shows particuhxily the decussation of the nervus terminalis (see also Sheldon '09, figs. 6 and 7); also the
commissura dorsalis, partly made up of fibers connecting the two partes supracommissurales of the precommissural body, partly of fibers connecting the two
nuclei olfactorii dorsales (commissura hippocampi, pars anterior). The relation
of the corpus precommissurale to the anterior commissure is brought out cleaily,
the pars commissuralis or commissure bed of Elliot Smith appearing ventrally
and the pars supracommissuralis dorsally.
36 Transection through the middle of the anterior commissure. Weigert
method. X 17. Shows especially the decussation of the tractus strio-thalamicr.s
cruciatus and of the tractus olfactorius medialis, pars lateralis; also the commissura hippocampi, pars posterior, presenting points of similarity, morphologically,
with the commissura dorsalis of Elliot Smith in amphibians, reptiles and mammals,
the commissura pallii of Kappers and Theunissen in amphibians, the commissura
pallii posterior of Edinger in reptiles, the commissui-a olfactorii internuclearis of
Goldstein, and connecting the nuclei pyriformes of the two sides. This section
also brings out several of the components of the medial forebrain bundle, the tractus olfacto-lobaris medialis of Kappers ('06). Dorsally, mingled with the fibers
of the commissura dorsalis are the fibers of the tractus hypothalamo-olfactorius
medialis. These are ascending fibers, part of which decussate in the anterior
commissure and part in the region of the nucleus posterior tuberis (see figs. 102,
104, 105). This is the tractus olfacto-hypothalamicus medialis of Goldstein.
com. ant., commissura anterior; co/h. dom., commissura dorsalis; co?h. dors.-\dec. Ir. hyp. olf. med., commissura dorsalis plus decussatio tractorum hypothalamo-olfactoriorummedialium;c'o//(. hi pp., pars post., commissura hippocampi,
pars posterior; corn, interbulh. {tr. olf. med., pars, med.), commissura interbulbaris
(tractus olfactorius medialis, pars medialis, the fibers of the tract forming the commissura interbulbaris (aut) ; Corp. precom., pars com., corpus jjrecommissurale, pars
supracommissiu-alis; dec. tr. olf. med.. pars lat., decussation of the tractus olfactorii mediales, partes laterales; dec Ir. strio-tlial. erne, decussation of the tractus
strio-thalamici cruciati; n. olf. lal., nucleus olfactorius lateralis; //. opt., nervus
opticus ; n . pi/r., nucleus pyriformis — this, together with a part of the nucleus olfactorius lateralis, corresponds to the lobus olfactorius posterior or area olfactoria
posterior lateralis of Kappers ('06), the lobus olfactorius posterior, pars lateralis
of Goldstein, the lobus olfactorius of Edinger ('08), the area olfactoria lateralis
of Kappers and Theunissen; n. term., nervus terminalis; palaeostr., palaeostriatum ; s. Urn. tel., sulcus limitans tclencephali ; s. ypsil.,fur. ant., sulcus ypsiliformis,
furca anterior; tr. hyp. olf. med., tractus hypothalamo-olfactorius medialis; tr.
olf. lat., tractus olfactorius l.-itcralis; //■. o//'. med.. jxirs. hil.. I r;u'tus olfactorius
medialis, pars lateralis; tr. olf. thai, med., i)(in< rent., tractus olfacto-thalaniicus
medialis, pars ventralis — this latter component of the medial forebrain bundle is
descending and made up of uncrossed fibers (see fig. 136), which, with the pars
intermedia, and p;irs dorsalis, form 1 he 1 racf us olfacto-lobaris medialis or tractus
olfacto-liNpot li.Ml.'iniirn- nicdi:ilis of l\:ipi)(Ts; //■. xl rio-lJial ., ti'actus sti'io-thalamicus.
270
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 8
5. lim.tel
.yp5il.fu^d,nt.
r. strio-thAl.
<;orp. precom..
com. dors.
■tr. olf. nned.,pe>.r3.
iAt.
n.term.
- ■ cofp.precom.,p<!M'5.
com.
com.interbulb,[t-rolf.
meci.,pa.f3.med.]
com. Ant.
'i^^yp^W^T>
■n.olf. !d.t.
, pCkla.eo5t-r
corp. precorn.,
pars 5upr2>.com.
' n. py*:"
tt: hyp. olf. med.
com. dors. + dec.
Ir. hyp. olf. med.
com. hi pp., pars post
tr. olf. thaA. med.,
pars vent.
dec. tv: olf med.,
P6JK3 IaI.
dec. tr. atrio-tha,!.
c-ruc.
Corp. pre com.,
P6.r5 com.
com. &.nt.
■nopt
271
PLATE 9
EXPLANATION OF FIGURES
37 Transection through the anterior commissure. Ramon y Cajal method.
X 40. Shows particuhirly the decussation of the tractus strio-thaUimicus cruciatus.
3S Transection through the anterior commissure. Toluidin blue method.
X 46. Shows with great clearness the limits of the pars supracommissuralis of
the corpus precommissurale, the sulcus limitans telencephali, the nucleus olfactorius dorsalis and the bed of the anterior commissure, the pars commissuralis of
the precommissural body.
corp. precom., pars coin., corpus precommissurale, pars commissuralis; corp.
precoin., pars SKpracom., corpus precommissurale, pars supracommissuralis; dec.
tr. hyv. olf. med. + com. hipp., pars post., decussatio tractus hypothalamo-olfactorii medialis plus commissura hippocampi, pars posterior; dec. tr. strio-thal.
cruc, decussatio tractus strio-thalamici cruciati; necl. com. lat., nucleus commissuralis lateralis; nucl. olf. dors., nucleus olfactorius dorsalis; riucl. olf. lat.,
nucleus olfactorius lateralis; nucl. pyr., nucleus pyriformis; nucl. teniae, nucleus
teniae, the nucleus taeniae of Edinger, Kappers and Goldstein; palaeoslr., palaeostriatum; rec. preopt., recessus preopticus; s. lim. tel., sulcus limitans telencephali; tr. fn/p. olf. med., tractus hypothalamo-olfactorius medialis; tr. olf.
med.. j)iirs. lal., tractus olfactorius medialis, pars lateralis; tr. olf. med., pars
lat. + com. trip J)., pars post., tractus olfactorius medialis, pars lateralis plus commissura hippocampi, pars posterior; tr. olf. that, med., pars, vent., tractus olfactothalamicus medialis, pars ventralis; tr. med. preopt., pars, ant., tractus medianopreopticus, pars anterior; tr. strio-thnl., tractus strio-thalamicus; tr. strio-thal.
incrtic. tractus st rio-llialainicus iticrucialus.
272
OLFACTORY CENTEH.S IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 9
medi6.n ca,vily.
tr. hyp. olf. med.
dec. tv. hyp. olf.med. + com. hipp.^pexrs post
iT. olf. med., p6>r5 le>.t.
tr. olf. tha.l.Tned., p6-t'5 vent.
ec. tr. strio-ths.!. cruc.
tr. 5trlo-th6,l.
K med . preopt., pa,r5. e^nt.
tr 5trio-th6l. incruc.
ec. pre opt.
37
nucl. olt. I5.L
or5.
orp. precom.,
pa,-r5 3upr6,com.
^Ir olf. med.,
•'. p6.r3. l6.t . +
i com.hipp.j
».pe).r3 post.
,corp. precom.,
pdxr5 com
38
273
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22. NO. 3
PLATE 10
EXPLANATION OF FIGURES
39 Sagittal section through the hemisphere. Golgi method. X 9. Shows
cells of the corpus precommissurale sending axones, the fibrae precommissurales
striaticae, into the palaeostriatum. Both ascending and descending fibers of the
tractus strio-thalamicus are shown; note especially the dichotomous branching
of the ascending neurites to form tangential fibers.
40 Cell of origin of the tractus olfacto-thalamicus mcdialis from the nucleus
medianus. Golgi method. X 94. From sagittal section.
41-42 Associationcellsof the nucleus medianus. Golgi method. X 93. From
sagittal section.
43 One of the neurones of the nucleus medianus, the neurite of which forms one
of the fibrae precommissurales striaticae. Golgi method. X 93. (See fig. 39.)
From sagittal section.
44 Cells of the palaeostriatum. Toluidin blue nietliod. X 575. From transverse section.
45 Neurone from cerebral hemisphere. Golgi method. X 93. From sagittal
section, neurite directed caudad, into tractus strio-thalamicus. This neurone can
hardly be assigned to a definite region, as it lies about midway between the typical
cells of the palaeostriatum and those of the area olfactoria lateralis. It will be
noted that its perikaryon is larger than that of typical cells of the area olfactoria
lateralis fmt that its dendrites do not show the conspicuous thorns of the typical
palaeostriatal neurones.
46 Cells of the dorsal ))ortion of the corpus ijverommissurale, i)ars supracommissuralis. Toluidin blue method. From transection. X 575.
47 Cells of the nucleus pyriformis. Toluidin blue method. From transection.
X 575.
48 Neurone from the nucleus olfartorius lateralis. Golgi method. X 93.
From sagittal section. This cell is found in the dorsal portion of the hemisphere,
adjacent to the nucleus olfactoriusdorsalis, but in the region calledepistriatum by
Johnston; its nciirile enters the tractus strio-l halainicus.
49 Neurone from the nucleus olfactorius lateralis. Golgi method. X 93.
J>om sagittal sell ion. This is found in the rostro-lateral jjortion of the hemi.sphere; it comes into association with the ascending fibers of the tractus thalamostriaticus as shown also in figs. 50 and 51.
////. inicoiii. >:lr.. fil)rac prccoriiiiiissuralcs slriatici; luib., habcnula ; //■. slriaIhiil.. tr;icti;s st rio-t liaiaiiiii-iis ; //•. l/nil . siriiit ., tractus thalamo-striaticus.
274
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 10
47 S ^"^
275
PLATE 11
EXPLANATION OF FIGURES
50-51 Neuronesof the palaeostriatum. Golgi method. X 185. From sagittal
sections. About the perikaryon of each neurone is a network formed by the
terminal arborization of the neurites of the ascending fibers of the tractus striothalamicus. The larger portion of the cells of the palaeostriatum are very thorny,
as shown in the cells drawn; a number of the neurones, however, particularly
those giving rise to descending fibers of the tractus strio-thalamicus, resemble
more closely fig. 45, with less conspicuous thorns and a larger perikaryon. The
cells shown in figs. 50 and 51 are evidently association cells; their processes extend
over a very large area, bringing different parts of the hemispheres into relation
with one another, with the thalamus and hypothalamus, and with the olfactory
apparatus through the precommissural body.
tr. Ihal. striiiL, tractus thalamo-striaticus.
27G
OLFACTUUY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 11
51
277
PLATE 12
EXPLANATION OF FIGURES
52 Neurone from the nucleus olfactorius lateralis, (iolgi method. X 93. From
sagittal section. This cell is found in the dorso-lateral portion of the hemisphere,
its neurite enters the tractus strio-thalamicus.
53 Neurone of the nucleus pyriformis. Golgi method. X 93. From sagittal
section. Most of the neurites from cells of this character and location enter the
tractus olfacto-hypothalamicus lateralis.
54 Transection through the region of the recessus preopticus. Kamon y ( 'ajal
method. X 46.
55 Transection through the caudal part of the anterior commissure. Weigert
method. X 17.
carp, precum., pars supracum., corpus precommissurale, pars supracommissuralis; n. opt., nervus opticus; nucl. com. lat., nucleus commissuralis lateralis;
rec. preopL, recessus preopticus; (r. hyp. olf. med., tractushypothalamo-olfactorius
medialis; tr. med. preopt., pars ant., tractus mediano-preopticus, pars anterior,
consisting of fibers originating in the anterior i)art of nucleus medianus and
terminating about the recessus preopticus; tr. iiivd. prcopl., pars post., tractus
mediano-preopticus, pars posterior, consisting largely of fibers originating in
the commissure bed and ending about the third ventricle in the region of the
nucleus preopticus; //■. alf. med., pars lat. +c. hipj)., pars post ., tnu^ius oUm-iovhis
medialis, pars lateralis plus commissura hippocampi, pars posterior; //■. olf. thai.
med., pars dors., tractus olfacto-thalamicus medialis, pars dorsalis; this component
of the medial forebrain bundle appears in this section for the first time in the drawings; tr. olf. thai, med., pars vent., tractus olfacto-thalamicus medialis, pars ventralis; tr. sirin-lhal . cnic., tractus strio-thalamicus cruciatus; tr. strio-thal. incruc.,
tractus strio-tlialaniicus incruciatus; tr. ten., tractus teniae, the tractus olfactohabenularis of Kaijpcrs. < loldstein, etc.
278
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 12
.median ca.vity.
o
o
At. 3lrio-tha.l. cruc.
i^r. med. preopt., pe^rs 6.nt.
■ ■ d. pre opt, p6.r5 poat.
vec. p^eopi.
/ k^xii:t;i^ ..^•■*^:-'^. •■•:>i;--- •:;i;^-: ;•*%> > .;:.• ^-. ?: ■ ;A •".;.
55
orp. pvecom..
pex+'S 3u.pr5.coTn.
en.
\ ^ ■ t^- olf. lha,l, nned.,pa,rs dors,
"tr hyp. olf. med.
Ir. ol f . in e d._, pars 16.1 . +
c.hipp., pdrs po5t.
tr olf. tha.1. med,, ph?(^ vent.
\.Y. 5trio-thM. cru-c.
tr slno-th6.1. incnac.
nucl. com. la^l.
n. opt.
279
PLATE 13
EXPLANATION OF FIGURES
56 Transection through the caudal part of the anterior commissure. Toluidin
blue method. X 46.
57 Cells of the nucleus teniae. Toluidin blue method. From transverse
section. X 575.
58-60 Neurones of the nucleus teniae. Golgi method. X 93. From oblique
sections, about midway between sagittal and transverse.
corj). precorn., pars com., corpus precommissurale, pars commissuralis; corp.
precom., pars supr acorn., corpus precommissurale, pars supracommissuralis;
nucl. cotn. Inl., nucleus commissuralis lateralis; nucl. olf.dors., nucleus olfactorius
dorsalis; nucl. pyr., nucleus pyriformis; nucl. ten., nucleus teniae; palaeostr.,
palaeostriatum; .S-. litu. tcL, sulcus limitans telencephali.
280
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 13
ucl.olf dors,
s.lim. tel.
y/. Corp. precom.p&rs.
iJ.'^Cf"- 3Upra.com.
|:|ittL^p.^^J^^nucP pyr
- '••.*• '• -»»v^V' . ' ^ . • '
- ' ,';■ • . " >■• ■ ■ - y! ' — tt^ t^-p *: :.. . '• ■ ' ■ ' ■ ■ ; — ; ^-^ — ,". .' '..'.f • >. : "> .•*• ?. jft' ..I .• ' ■'•' '
••V-r'-'-' Ji^ii^^vl-nucl . len.
^^^^/^%-^^SSC:*^55S: v'^ . ': .' ' ■■^^■^%-^;^\fiS'lC.^^o'^P- pre com.
nucl.com. la^t.
PLATE 14
EXPLANATION OF FIGURES
61 Transection through the caudal part of the anterior coinmissure. Weigert
method. X 17.
62 Sagittal section slightly to one side of the median line, showing the tractus
preopticus superior. Golgi method. X 46. The location of the different parts
of the nucleus preopticus is indicated by broken lines.
63 Neurone of the tractus preopticus superior. CJolgi method. X 93. From
sagittal section. (See fig. 62).
64 Cells of the nucleus preopticus, pars parvocellularis anterior. Toluidin
blue method. X 575.
65 Cells of the nucleus entopeduncularis. Toluidin blue method. X 575.
Corp. precom., ixir.scum., corpus preeommissurale, pars commissuralis; corj>. precox., pars supracum., corpus preeommissurale parssupracommissuralis;/r;.sf. ///(J.
hem., fasciculus medialis hemisphaerii; n. opt., nervus opticus; nucl. prcopl.. pars
parvocell., nucleus preopticus, pars parvocellularis; opt., optic chiasma; j)ars inagnoceZ/., pars magnocellularis of the nucleus preopticus; pars parvocell. post., pars
parvocellularis posterior of the nucleus preopticus; rec. preopt., recessus preopticus. tr. hyp. olf. med., tractus hypothalamo-olfactorius medialis; Ir. iilj. Ihal. incd.,
pars dors., tractus olfacto-thalamicus medialis, pars dorsalis; //■. alf. Ihal. incd.,
pars voiL, tractus olfacto-thalamicus medialis, pars vcntialis; //•. iii(d. pnopl.,
pars ant., tractus mediano-prcopticus, pars anterior; Ir. prcapl. sup., tractus
preopticus superior; the connections of this tract arc fully shown in the figure;
it is apparently, Goldstein's tract X (Taf. 11, fig. 7) ; //•. slria-llinl. i ncnic, tractus
strio-thalamicus incruciatus; //•. ten., tractus teniae.
282
OLFACTORY CENTERS IN TELEOSTS
RALPH EUWARD SHELDON
PLATE 14
^■^corp. precom., pA-rs
■;. ;-• • . :-Xj::^;' 5upr& com
•v^^fV'^^n^' ■'•'•Ir. olf. lbl^l .med., p6.V5 .
-"'■■' ;.-V:.v-7' vent.
■.jVlln olf. tha.1. med., p&^r5
f. •-:••■ dors.
- ■ Ir. hyp. oU. med.
Corp. pre com., pa.r5.com
Ir. 5tno-tha),l. incruc.
_tr med. preopt.,p5,r3.
nucl pre opt p«.-r5.
paxrvocelj.
n.opt.
65
283
PLATE 15
EXPLANATION OF FIGURES
66 Transection through the cerebral hemispheres caudal to the anterior commissure. Toluidin blue method. X 46.
67 Transection through the cerebral hemispheres slightly caudal to the level
shown in fig. 66. Toluidin blue method. X 46. Shows particularly the rostral
portion of the pars magnocellularis of the nucleus preopticus and its relation to the
pars parvocellularis.
corp. precuni., pars intcrmed., corpus precommissurale, pars intermedia; this,
the caudal prolongation of the pars supracommissuralis, meets the nucleus pyriformis at the posterior pole of the hemisphere, it likewise comes in close contact
with the extension of the pars commissuralis caudally and ventrally, the pars parvocellularis of the nucleus preopticus; /asc. lat. hem., fasciculus lateralis hemisphaerii, the lateral forebrain bundle; consisting of the tractus stiio-thalamicus, tractus thalamo-striaticus, tractus olfacto-hypothalamicus lateralis and
tractus hypothalamo-olfactorius lateralis; fasc. vied, hem., fasciculus medialis
hemisphacrii, the medial forebrain bundle; nucl. entoped., nucleus entopeduncularis; nucl., preopt. pr/r.s- magnucell., nucleus preopticus, pars magnocellularis;
riurl. prropi.. parfi purvucell., nucleus preopticus, pars parvocellularis anterior;
niirl. pur.. luicleus pyriformis ; unci. ten., nucleus teniae ;.s. lini. (el., sulcus limitans
telencephli; .s. ijp.nl., fur. ant., sulcus ypsiliforniis, furca anterior.
284
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 15
' '*' .■.." .v':,'^ //»/<•.•.'
). ypsil. fur. 6.nt.
coyp. precom.
pd/-^. inlermed.
nucl. pyK
.^fitei
nucl. ten.
ucl.preopt., p6.r5.
p6.rvocell.6>nt.
P5.r5. intermed.
d. hem.
pa^rs. pa^rvocell.
n.
. hem.
toped.
p£).r5.rne^<gnocell.
,pAr5. ps^rvocell.
285
PLATE 16
EXPLANATION OF FIGURES
68 Transection, ;it the level of the chiasma. Weigert method. X 17.
69 Transection at approximately the same level as shown in fig. 68. Ramon y
Cajal method. X 46.
carp, precom., pars intermed., corpus precommissurale, pars intermedia; fasc.
lat. hem. < >, fasciculus lateralis hemisphaerii; fasc. vied. hem. < >, fasciculus
medialis hemisphaerii; nud. entoped., nucleus entopeduncularis; nud. preopt.,
pars magnocell,, nucleus preopticus, pars magnocellularis; nucl. preupt., pars
parvocelL, nucleus preopticus, pars parvocellularis; nud. pyr., nucleus pyriformis;
sac. dors., saccus dorsalis;s. ypsil.,fur. post., sulcus ypsiliformis, furca posterior; tr. hyp. olf. med., tractus hypothalamo-olfactorius medialis; Ir. olf. hyp. lat.
< >. tractus olfacto-hypothalamicus lateralis; //•. olf. Ih(d. iticd., pars dors.,
tractus olfacto-thalamicus medialis, pars dorsalis; //■. olf. thai, mcd., pars vent.,
tractus olfacto-thalamicus medialis, pars ventralis; tr. opt., tractus opticus;
tr. praeth. cin., tractus praethalamo-cinereus of Kappers; tr. preopt. entoped.
- — — >. tractus preoptico-entopeduncularis; tr. preopt. intermed., pars ant. < >,
tractus preoptico-intermedius, pars anterior; //■. preopt. intermed.. jiars lot.,
tractus preoptico-intermedius, pars lateralis; //•. strio-thal. cruc. < >, liactus
strio-thalamicus cruciatus; Ir. ^trin-thal. incruc. < >, tractus strio-thalamicus
incruciatus; //•. Iin.. tractus teniae.
286
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 16
m. 5exC. dors.
Corp. precom., ^6-r3 inlermed.
nucl. pyr.
tr. ten.
tr. olf. Ihexl. med.^pexrs dJoji
tr hyp. olt. med
tr olf. thesl.med., p&^rs vent.
nucl. entoped.l
nijLci. preopt., p6-rs mex^nocell.
tr. preopt. intermed., p5.r5 \^l.
nucl.preopt., pe>.r5 p6>rvocell.
tr. opt.
If. hyp. Kt.<-^
Veopl intermed., p6.r3.
d.nt.-e-^
&.5C. med. hem.«->
r 5trio-tha.l crac.<— ;
nucl. entoped. -e-^
ir preopt entoped
tr strio-thexl mcruc.<
tr preopt Intermed.,
p6.r5 \iX.
tr prdxeth cin,
.opticus.
287
PLATE 17
EXPLANATION OF FIGURES
70 Transection through the posterior pole of the hemisphere ;in(l the nuchuis
magnocellularis. Toluidin blue method. X 46.
71 A group of cells of the nucleus magnocellularis. Toluidin blue method.
X 575.
72 Transection slightly caudal to the level shown in fig. 69. Ramon y Cajal
method. X 46.
fasc. vied. hem. < — — >, fasciculus medialis hemisphaerii; tiucl. entoped., nucleus
entoi)eduncularis; 7iucl. intermed., nucleus intermedius; nucl. preopt., pars
magnocelL, nucleus preopticus, pars magnocellularis; rtucl. preopt., pars parvocell.
lat., nucleus preopticus, pars parvocellularis lateralis; tr. entoped. hah., tractus
entopedunculo-habenularis; tr. olf. hyp. lat. < >, tractus olfacto-hypothala
micus lateralis; tr. praclh. cin., tractus praethalamo-cinereus; tr. preopt.
entoped. < >, tractus preoptico-entopeduncularis; tr. preopt. intermed., pars
lat., tractus preoptico-intermedius, pars lateralis; tr. preopt. intermed., pars med.
< >, tractus preoptico-intermedius, pars medialis; tr. strio-thal. cruc. < >,
tractus strio-thalamicus cruciatus; tr. strio-thal. incrur. < >, tractus strio-tha
lamicus incruciatus; //•. ten., tractus teniae.
288
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 17
ucl. intern>ed.
/ ■^ ^^nucl'. entoped.
-•■'4^^...^^'.^^^
i^&i.^:V§i?^'
vLcl.pi'eopt.,pa-f5 Tr\a,^nocell.
eopt., p6.t-3 p6.rvoceU.l6t.
hyp. l2vl. ^-^
opt. intermed., pA.'t^s med.ntoped . h&b.
MTied.hem.'^-^
3tno-lh4>.l. cruc.-^->
cl. entoped.
pveopt.mtenned., pexv:5. la^t.
pKeopt. entoped. <-^
5trio-tha>l. incruc.<-^
cin.
)t., p^r5 Tn5.^nocell.
cin.
THE JOURNAL OF COMPAR.VTIVE NEUROLOGT, VOL. 22, NO. 3
PLATE 18
EXPLAXATIOX OF FIGURES
73 Transection at the level of the commissura transversa. Weigert method.
X 17.
74 Transection through the same region as is shown in fig. 73. Ramon y Cajal
method. X 46. Shows particularly the tractus preoptico-habenularis, pars
lateralis. In Petromyzon, according to Johnston ('02), a large portion of the fibers
of his tractus olfacto-habenularis (my tractus preoptico-habenularis) take this
course; as is also the case, but to a lesser extent, in amphibians and reptiles (Herrick, '10 b).
75 Cells of origin of the fasciculus retroflexus, or Meynert's bundle. Golgi
method. X 93. One of the cells possesses a long neurite which may be traced into
the fasciculus retroflexus.
com. tranfi., commissura transversa; fasc. lat. hem. < >, fasciculus lateralis
hemisphaerii; /V;.sr. incd. hem. < >, fasciculus medialis hemisphaerii ; /asc. med.
It. opt., fasciculus medialis nervi optici; hah., habenula; nitcl. preopt., 2^ffrs
magnocelL, nucleus preopticus, pars magnocellularis; pol. j)<)st. hem., polus
posterior hemisphaerii; Ir. hyp. olf. med., tractus hypothalamo-olfactorius
medialis; tr. olf. hub., tractus olfacto-habenularis; tr. olf. thai, med., pars dors.,
tractus olfacto-thalamicus medialis, pars dorsalis; //•. (df. thai, med., pars
hdermed. < >, tractus olfacto-thalamicus medialis, purs intermedia; tr. olf.
thill, med.. j)ar.s re)/t.. tractus olfacto-thalamicus medialis, pars ventralis; tr. opt.,
tractus ()])ticus; //•. praelh. ein., tractus praethalamo-cinereus; tr. preopt. hah.,
partes nut. it med., tractus preoptico-habenularis, partes anterior et medialis;
Ir. preopt. hah., pars lat., tractus preoptico-habenularis, pars lateralis; tr. preopt.
hah., pars post., tractus pre()i)tico-hat)eiudaris, ))ars posterior;//-, preopt. intermed.,
pars. Int., tractus pi'eo))! ico-iiif cniiedius, i)ars latci-alis.
290
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 18
ki^vt?'^-'
^'r-|^*^
73
pol. po5t. hem.
t*-. olf hdvb
tK pveopl ha-b.,
pfiKftes anl. et med
\i' hyp. oH. med.
tr olf. Ih6.1. med.,
P<5,r5 mtermed.
tr olf. th&l. med.,
p6.r5 dors.
r, olf. Ihexl. med.,
pa.V"5 vent
nucl. preopt.,
pe)^r5 ma^^nocell.
ta.sc la.t. hem.
t-r. opt.
tv. p-)r6,eth. cin.
tr preopt. intermed.,
p&rs last
tr. pre^eth. cin.
fa^sc. mied. n. opt.
com. tres,ns.
—ir olf. hJ^b.
eopt. ha.b., p6~r5 post,
med. hem. ^^
la.1. hem. <-^
opt.
pr<i,eth cin.
c. med. n opt.
preopt. he>.b., pars la>t.
cm. trAns. ,,
^'-^^^ 75
291
PLATE 19
EXPLAXATIOX OF FIGURES
76 Transection through the ganglia habenularum. Weigert method. X 17.
77 Transection at the level of the commissura horizontalis. Weigert method.
X 17.
a, fibers, originating largely in the nucleus posthabenularis and apparently
entering the optic tract (described as an optic connection by Bela Haller); com.
hah., commissura habenulai'is, containing also decussating fibers of thetwotractus
olfacto-habenulares; com. Herrick, commissura Herricki; coin, horiz., commissura
horizontalis of Fritsch; com. trans., commissura transversa; corp. gen. lat., corpus
geniculatum laterale;/o.sc. lat. hem. < >, fasciculus lateralis hemisphaerii;/asc.
med. n. opt., fasciculus medialis nervi optici; /osc. retr., fasciculus retroflexus;
fib. tect. n. opt., fibrae tectales nervi optici (centrifugal); hab., habenula; lob. inf.,
lobus inferior; nucl. preopt., pars parvocell. post., nucleus preopticus. pars parvocellularis posterior; nucl. prerot., nucleus prerotundus; nucl. vent, tub., nucleus
ventralis tuberis; tr. hab. dien . < >, tractus habenulo-diencephalicus; this is the
'tractus habenula ad diencephalon' of Goldstein; tr. hyp. olf. med., tractus hypothalamo-olfactorius medialis; tr. olf. hab., tractus olfacto-habenularis; tr. olf.
thai, med., pars dors., tractus oUacto-thsxlamicus medialis, pars dorsalis; tr. olf.
thai, med., jxirs intcrmed. < >, tractus olfacto-thalamicus medialis, pars intermedia; tr. olf. thai, med., pars rent., tractus olfacto-thalamicus medialis, pars ventralis; tr. opt., tractus o])ticus; tr. pructh. ciu., tractus praethalamo-cinoreus.
292
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 19
•*V*
tectum,
com. ha.b.
fib. tect.-n. opt.
tr. hyp olf. med.
tr. olf. tha,V med.,
pa.rs dors.
Ir. o\i. the..!, med.,
p£>>rs mtermed.
tr. olf. tha.1. med..
pi^r5 vent,
■f&^sc. 16,1, hem.^->
f6.sc. med. -n opt.
t^. p^'6>eth. cm.
com. l+-(5,n5
%>f
77
cov^ <gen. ]a>.t^
hAb.
fe^sc. retir. .^'
fib. tect. n. opt, ' "' ~
\r. oU. ha.b.
a..
if. h3>b. dien. ^-^
tr. hyp. olf. med._^::~--^
, Ir opt .
tr. olf. th.^1. med., pars dors
tr. olf. tha.1. med., p&>.r3 mtermed
tr. olf, th6«l. med., pexrs vent.
fa.3c. l^t. hem,*—?,
nucl. pfeopt., ps.rS' pArvocell. post
f6sc. med. n. opt.
com. Merrick. i\
tr. preveth. cin. '
com. trains.
com. horiz.
lob. inf.
nu-cl . prerot
orwicl. vent, tub
293
PLATE 20
EXPLANATION OF FIGURES
78 Transection Ihi-ough the ganglia habcmilanini. Toluiilin hluc met hod.
X 4().
coin, horiz., commissura hoiizontalis; cori). i/cii. hiL, corjjiis genieulatuni
laterale;/(7;. ans., fibrac ansulatae; hub., habenula, showing characteristic arrangement of cells; hyp., hypophysis; lob. inf., lobus inferior; nucl. ant. thai., nucleus
anterior thalami of Goldstein; nucl. posihab., nucleus posthabenularis, 'Das
posthabenulare Zwischenhirngebiet' of (Goldstein, 'Die posthabenulare Zwischenhirngegend' of Bela Haller; nucl. preopl., jxirs parvocell. post., nucleus prcojiticus.
pars parvocellularis posterior; nucl. prcmt., nucleus prerotundus; mirl. voil. tub.,
nucleus ventralis tubcris.
294
OLFACTORY CENTERS IN TELE08TS
RALPH EDWAUD SHI.I.DON
PLATE 20
i■^^<^^^.V fly
_h5.b.
v^"' ^fi:^-: '^'^i;.'.;' ■ v-'^.--^;- -'^V::- -^'•-•^;.
nucl. postna-b.
^:}-.' '^'IviV •:/"■ ;j- 'y - .-'^;- •>^:^'-^'-^'f'^r/^ Corp. <3en.l5.t.
vy.' i Sy
Lnucl. e/nt. thexl.
nuLicl preopt.,pa.v^.
.. •••.x-v---, ,.-.-.■. A /pa-rvocell. post.
-fib. d>n3.
•"•'"■' .•■••• . ';■■■ nu.r.1. prerot.
I coin, "hori? V
•^r^, 't^a.t
riucl verit. tub.
295
PLATE 21
EXPLANATION OF FIGURES
7L» Transection slightly caudal to the level shown in fig. 77. Weigert method.
X 17.
80 Transection through the nucleus anterior tuberis. Weigert method. X 17.
a, see fig. 76; com. Herrick., commissura Herricki; com. horiz., cominissura horizontalis; com. post., commissura posterior; com. trans., commissura transversa;
Corp. gen. lat., corpus geniculatum laterale; fuse. hit. hem.< >, fasciculus lateralis hemisphaerii ; /asc. 7ned. n. opt., fasciculus medialis nervi optici; /a.5c. retr.,
fasciculus retroflexus; ^6. cms., fibrae ansulatae; ./(6. tect. n. opt., fibrae tectales
nervi optici; hab., habenula; hyp., hypophysis; lob. inf., lobus inferior; nucl. ant.
thai., nucleus anterior thalami; nucl. ant. tub., nucleus anterior tuberis; nucl. lat.
tub., nucleus lateralis tuberis; 7iucl. j>rerot., nucleus i)rerotundu.s; nucl. rent, tub.,
nucleus ventralis tuberis; tectum, tectum opticum; tor. long., torus longitudinalis;
tr. hab. dien.<: >, tractus habenulo-diencephalicus; //•. hyj). olf. )ucd., tractus
hypothalamo-olfactorius medialis; tr. olf. thai. nud.. pars dors., tractus olfacto
thalamicus medialis, pars dorsalis; tr. olf. thai, nied., pars intermed.< >, tractus
olfacto-thalamicus medialis, pars intermedia; tr. olf. thai, med., pars vent., tractus
olfacto-thalamicus medialis, pars ventralis; tr. opt. tractus opticus, <?■. praeth. cin.,
tractus practhalamo-cincreus; tr. strio-thal. incruc.< >, tractus strio-thalami
cus incruciatus; tr. tub. dors., tractus tubero-dorsalis; valvula, valvula cerebelli.
296
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 21
co'rp. <gen. la,t. " .
fib. tect. n. opt.
ha,b.
fe^sc. retr:
Sk ..^^^
tr. hf^b. dien..e^
tir-. hyp. olf. med
t-r, olf. thai, med., pi^rs Intermed. <-»
tr. olf. thai. Tned... pi^rs dors
tr olf. tha,l. med., p&rs vent
tr opt.
te^sc. la,t. hem.'^-^
com. ■^^ev^^icK.
fd.sc. med. n. opt.
t^' prð. cm.
com. tirevne>.
com. hoviz..
lob. mf.
niacl pret-ot. yf
nucl. VGnt. tub
com. post.
fib. tect. n. opt.
h&b ,^^
fd^sc. retr
nucl. 6.nt. th6>l.
Corp. <^en. led.
tr. opt.
tr hc^b. dien. ^^
tr. hyp. olf. med.
■'■ tr olf. thAl med.,pe>r5 dors.
tr. olf. thd>l. med., p6>r5 mtermed.
tr olf. thavl med., p6.r5 vent,
com. tr&ns.
fib. e^na
lob. mf.
nucl. prerot.
tr. strio- thevl. incruc. <-^
' com. horiz.
j tr tub. do-rs
, il'-Tiucl. &,nt. tub.
9. tr pra^eth. cm.
nucl. le^t. tub.
nucl. vent. tub.
• '-^ hyp.
297
PLATE 22
EXPLANATION OF FIGURES
SI Transection through the nucleus anterior tuberis. Toluidin blue method.
X46.
com. trans., commissura transversa; cori). gru. hil., corpus geniculatuni laterale; hab., habenula; hyp., hypophysis; lob. hrf., lobus inferior; nucl. ant. thai..
nucleus Sinterior thai ami; nucl. ant. tub., nucleus anterior tuberis; nucl. po.^th ah.,
nucleus posthabenularis; nucl. prerot.. nucleus prerotundus; nucl. rent. tul>.,
nucleus ventralis tuberis; tr. opt., tractus opticus.
298
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 22
» ^ 4 ^ i-" r y »• '■ ' •
xorp.A^en. la.t.
- ^ -iSr^
"^ -."^^^ t^y opt .
-Com. Irdv.n5.
^\^^J^|||f^^t
_nu.cl. pverot.
■•. ..;.v :.■ ■■■■■ :••-■, ^ '^--^
v" . ■■■"•; ':M
pSjiS-StS;^^ ' y:- ^-M W cl-^nt
tub.
.lob. inf.
tub.
299
PLATE 23
EXPLANATION OF FIGURES
82 Transection slightly caudal to the level shown in fig. 80. Weigert method.
X 17.
83 Transection through the rostral end of the nucleus rotundus. Weigert
method. X 17. Shows particularly the connections between the fasciculus lateralis hemisphaerii and the nuclei prerotundus, rotundus and diffusus lobi lateralis.
a, (see fig. 76) ; cor p. gen. lut., corpus geniculatumlaterale; com. /ionz., commissura
horizontalis; cow. post., commissura posterior; com. trans., commissura transversa;
fasc. retr., fasciculus retroflexus; ^ifc. ans., fibrae ansulatae; fib. tect. n. o/^/.,fibrae
tectales nervi optici; /i?/p. hypophysis; ?o6. fn/., lobus inferior; nud. out. thai.,
nucleus anterior thalami; Jiucl. ant. tub., nucleus anterior tuberis; ntici. lot. tub.,
nucleus lateralis tuberis; nucl. prerot.. nucleus prerotundus; nucl. rot., nucleus
rotundus; nucl. vent, tub., nucleus ventralis tuberis; tr. cbl. tect. + com. horiz.,
tractus cerebello-tectalis plus the commissura horizontalis; tr. hub. dicn.< >,
tractus habenulo-diencephalicus; //■. hyp. olf. med., tractus hypothalamo-olfactorius medialis; <r. olf. hyp. lat. + tr. strio-thal. cruc, tractus olfacto-hypothalamicus lateralis plus the tractus strio-thalamicus cruciatus; tr. olf. thai, itied., p<rrs
dors., tractus olfacto-thalamicus medialis, pars dorsalis; tr. olf. thai, incd., pars
intermed.< >, tractus olfacto-thalamicus medialis, pars intermedia; tr. olf. thai.
med., pars vent., tractus olfacto-thalamicus medialis, pars ventralis; tr. opt.,
tractus opticus; tr. praeth. cin., tractus praethalamo-cinereus; tr. rot. lent., tractus rotundo-lentiformis (Kappers); tr. strio-thal. iiicruc.< >, tractus striothalamicus incruciatus; shows particularly the fibers innervating the nucleus
diffusus lobi lateralis; //■. thai, niani., tractus thalamo-mammillaris (Goldstein);
tr. thai, sp., tractus thalaiii(i-si)iiia]is f Kappors) ; /r. /»/;. r/o?-,v., tractus tubero-dorsalis.
300
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 23
.-r-g^^^
com. post.
f^5c.reir.
nucl. e^nt. th&l.
orp. gen, la-t.
tr. ha.b.dien.^-^
tt. hyp. o\t. med.
tr. olf. tha,l. med.,pa.r5. mtermed.
tr. olf.lha.l.med..ps>.r5. dors,
tr. opt.
tf. olf. Ihsxl. Tried., p6.r5. vent,
com. \'!r^r\5.
fib. £xn5.
te sli'io-lha^l incruc.< — >
com. honz.
nacl.prerot.
tr. tab. dor.5.
nucl. 6nt. tub.
tr 5trio-lh5b mcruc ^-^
V nucl. l5.t. tub.
tr pr<5.eth. cm.
niicl. vent. tub.
lob. mf,
hyp.
tr cbl. tecl.+ com.hoviz
tr rot . lent.
t5.5c. retr
fib. tect. n. opt.
2k.
tr tha.1 ma>>m.
tr tha-b 5p.
tr opt.
com. tr5.n3.
trha.b.dien <-^
tr hyp.olf.Tned.
tr. oil tha.bTined.,pe»<^'e). dors.
tr. olf. hyp. levl.+ tr st.rio-ths.t cruc.
tr olf.thM. med.^p&rs. vent.
nucb prerot.
tr. sine -thM. mcruc. -e^
nucl. n?t.
com.horiz.
tr tub. dors.
lob.jn^l^
301
PLATE 24
EXPLANATION OF FIGURES
84 Transection through the rostral end of the nucleus rotundus. Toluidin
blue method. X 46.
85 Cells of the nucleus prerotundus. Toluidin blue method. X 575. From
the right nucleus. Shows the scattered arrangement of the cells and their difference in size.
86 Neurones of the nucleus prerotundus. ( lolgi method. X93. From sagittal section.
b, cells adjacent to the recessus lateralis hypothalami (see fig. 87); coni.
irans., commissura transversa; fasc. retr., fasciculus retrofiexus; nucl. aid. tub.,
nucleus anterior tuberis; 7iucl. dif. lah. Int., nucleus diffusus lobi lateralis;
/(//'•/. hit. tub., nucleus lateralis tubeiis; iiucl. pustluil)., nucleus posthabenularis;
nucl. prerot., nucleus prerotundus; nucl. rat., uuchnis rotundus ; nucl. vent, tub.,
nucleus ventralis tuberis.
302
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
V
85
303
PLATE 25
EXPLANATION OF FIGURES
87-88 Neurones of the nucleus prerotundus, Golgi method. X 93. From sagittal sections.
89 Transection immediately caudal to the level of the commissura posterior.
Toluidin blue method. X 46.
90 Cells of the nucleus rotundus. Toluidin blue method. X 575. Shows the
typical arrangement of the cells in scattered groups.
com. post., commissura posterior; fasc. retr., fasciculus retroflexus; 7iucl. ant.
tub., nucleus anterior tuberis; nucl. cbl. hyp., nucleus cerebellaris hypothalami;
• nucl. dif. lob. lat., nucleus diffususlobilateralis;?ii/cL prerot., nucleus prerotundus;
nucl. rot., nucleus rotundus; rec. lat. hyp., recessus lateralis hypothalami.
304
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 25
-com.po5t.
J6.3c.reti:
•"• ' - ^^'S\ e -:4iy *'■■'"- '^ '-' '- »- ' ^"h^ii
'nucl.rot.
nuclJcbl.hyp.
Inucl.Ant.
tub.
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3
PLATE 26
EXPLANATION OF FIGURES
91-94 Neurones of the nucleus rotundus. Golgi method. X 93. From sagittal sections.
95-99 Neurones from different parts of the lobi laterales. Golgi method. X
93. From sagittal sections. Fig. 95 is taken from the caudal angle of the lobe,
fig. 96 from the ventro-medial area, fig. 97 from the latero-medial, figs. 98 and 99
from the ventral area proper.
100 Transection at approximately the same level as that shown in fig. 89.
Weigert method. X 17.
com. horiz., commissura horizontalis; cu)it. post., commissura posterior; com.
trans., commissura transversa; fasc. retr., fasciculus retroflexus; nucl. ant. tub.,
nucleus anterior tuberis; itucl. dif. lob. lat., nucleus difTusus lobi lateralis; nwc/.
prerot., nucleus prerotundus; nucl. rot., nucleus rotundus; ir. cbl. tcrl. + com.
horiz., tractus cerebello-tectalis plus commissura horizontalis; tr. hab. dien.
< >, tractus habenulo-diencephalicus; ^r. hyp.olf. vied., tractus hypothalamo
olfactorius medialis; tr. olf. thai, med., pars dors., tractus olfacto-thalamicus
medialis, pars dorsalis; //•. olf. thai, med., pars vent., tractus olfacto-thalamicus
medialis, pars ventralis; tr. rot. lent., tractus rotundo-lentiformis; tr. strio-thal.
cruc.+ tr. olf. hyp. Zoi., tractus strio-thalamicus cruciatus plus tractus olfactohypothalamicus lateralis; tr. thai. mam., tractus thalamo-mammillaris; tr. thai.
sp., tractus thalamo-spinalis.
306
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 26
100
tr ro\: lent.
i'r. cbl. tect + com, horiz.
com. post.
f55c. -retr.
t-r. tho.1. ■m&.Tn.
tr. th<5d 5p.
com . tv<Mns.
tr. hd>b. dien.<— >■
ir. hyp. olt.med
nucl. pKerot.
t?< strio-the^l. crac. + ti^ olf.
hyp. la.t.
1+: olf. t.he>.l.med., pa^rs dors.
tr. oil thd.l.med. p6>r5' vent,
nucl. rot.
com. horiz.
ri.ucl.6>nt. tub.
rruxTTdif. lob. ]^t.
307
PLATE 27
EXPLANATION OF FIGURES
101 Transection sliglitly caudal to the level shown in fig. 100. Weigert
method. X 17.
102 Transection through the decussation of the tractus hypothahimo-olfactorii
mediales. Ramon y Cajal method. X 46.
com. horiz., commissura horizontalis; com. post., commissura posterior; co7n.
tr(ini<., commissura transversa; dec. tr. hyp. olf. med., decussatio tractorum olfactorionmi medialium;/asc. retr. fasciculus retroflexus; lob. lat. hyp., lobus lateralis
hypothalami; lob. med. hyp., lobus medialis hypothalami; nucl. dif. lob. Int.,
nucleus diffusus lobi lateralis; nucl. prerot., nucleus prerotundus; nucl. rot.,
nucleus rotund us; nucl. subrot., nucleus subrotundus; rec. lat. hyp., recessus
lateralis hypothalami; tr. cbl. tect. + tr. rot. lent. + com. horiz., tractus cerebellotectalis plus tractus rotundo-lentiformis plus commissura horizontalis; tr. hab.
dien.< >, tractus habenulo-diencephalicus; tr. hyp. <ilf. med., tractus hjpo
thalamo-olfactorius medialis; tr. olf. thai. nieiL, pars dors., tractus olfacto-thalamicus medialis, pars dorsalis; tr. olf. thai, med., pars rent., tractus olfactothalamicus medialis, pars ventralis; tr. rot. lob., tractus rotundo-lobaris; tr. striothal. cruc. + tr. olf. hyp. lat., tractus strio-thalamicus cruciatus plus tractus
olfacto-hypothalamicus lateralis; tr. thai, mam.., tractus tlialanio-inanunillaris; tr.
thai, sp., tractus thalamo-spinalis (Kappers).
308
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 27
com. post
tn cbl. lect +tr. fot. lent. +
com. ho-i^iz..
fa.sc. retr.
tr. ibcvl. sp.
ti'. thfi.!. m&m.
com. lra>.n£>.
ntxcl. pyne+'ot.
tt-. hyp. oil med
tr. 5t4'io-th2>,l. cruc.+
t*-. olf. hyp. la,l.
t+-. hAb. dien. -e-^
nucl. t-ol.
tr. oH. thsvl. med., p6r5 dors.
tr. olf. thd-l. med,, pair's vent.
com. horiz.
t*-. fot. lob.
rec. la.l.hyp.
lob. ]d,t.hyp.
Job.med . hyp.
G^^ii-cl- d if. lob. la.t.
101
nucl. prerot.
nuLcl. rot.
ucl. subrot.
ec. t^ hyp. olf. med.
309
PLATE 28
EXPLANATION OF FIGURES
103 Transection tlii-ougli the nucleus posterior tuberis. Toluidin blue method.
X 46.
104 Obliciue longitudinal .section showing the origin of the tractus hyi)othalamo-olfactorius medialis. Golgi method. X 9.
105 Neurone of originof the tractushypothalamo-olfactoi'iusmedialis. Golgi
method. X 93. Taken from same section as fig. 104.
chiasma, ojitic chiasma; corp. precom., corpus precommissurale; cms ulf., crus
olfactorium; n. opt., nervus opticus; nucl. cbl. hyp., nucleus cerebellaris hypothalami; nucl. dif. Job. [at., nucleus diffusus lobi lateralis; 7tucl. post, thai., nucleus
posterior thalami; nucl. post, tub., nucleus posterior tuberis ; nucl. prerot., nucleus
prerotundus; nucl. vol., nucleus rotundus; rec. lat. hyp., recessus lateralis hypothalami; .sac. vase, saccus vasculosus; tela, membranous roof of forebrain; tr.
chl. hyp., tractus cerebello-hypothalamicus; tr. hyp. olf. mciL, tractus hypothalaino-olfaclorius medialis; tr. <>]>t., tractus ()j)ticus; tr. stria-lhal.. tractus striothalainicus; //•. thai, sir., tractus thalamo-striaticus; ralruhi. valA'ula cerebelli.
310
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 28
nucl. prerot.
nucl. rot.
^ nucl/po3t. th&l.
nucl. cbl. hyp.
rec. la.1. hyp.
\rn|icl.dif. lob.
la,t.
lucl.post
^;:-<i:ijr'
-.'<^"-J
103
ve>.lvuld>
^SiiiiiiiailiJ'V
t^^. hyp. olf. med
nucl. post tub^
.r. cbl. hyp.
■£xc. veKSC.
neurite.
com
ru3 olf.
chie^smd..
-tr. tha-1. 3t^
105
104
311
PLATE 29
EXPLANATION OF FIGURES
106 Transection thiouj;;!! the Haubenwulst. Toluidin blue method. X 46.
107 Transection through the nucleus subrotundus. Toluidin blue method.
X -17. Detail cells. X o75. Shows the characteristic groupingof thecellsin the
center of the nucleus (sec fig. 106). From right side.
108 Cells of the nucleus cerebellaris hypothalami. Toluidin blue method.
X 575. Shows tyi)ical scattered arrangement of the cells (see figs. 103 and 106).
nucl. cbl. hyp., nucleus cerebellaris hypothalami; nucl. dif. lob. lat., nucleus
diffusus lobi lateralis; nucl. fasc. long, med., nucleus fasciculi longitudinalis
medialis; nucl. post, thai., nucleus posterior thalami; nucl. prerot., nucleus
prerotundus; nucl. rot., nucleus rotundus; nucl. subrot. nucleus subrotundus;
rec. l(it. hijp., recessus lateralis hypothalami.
312
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 29
■^*/-;^Vr\.- -7 '^j.';-:""v:"'^V^-:;.:^'/;-" . ••;;■; K^ \■^\^^^■ti^i^■l^C$^^■
.;...-.,...,•.,.•.■', .» •, J. •••••..•., • . ■.. ■ • - . :•»"•••:!;/;-:,
■■•■ ,\ ^. • '■.■'.• * '"•,'•*- - •■V'" •■••■-•■".'. '■'• ■ '• :f?J!i"
. . ■■ : •;* ■ ■ ■■'.'• • • ,'• '■ •-.'.. ^ • V*"- •^ " . ■• . ■ :: ,' -i'. • V r".;-.'.t;ii.'.
•'■" :»J ■' , ;^ '••■■:% ' '-*' '"■, -" . ;;.•'-■'.'•'■ '-i^W
t5>5c. lon($.
- ivnucl.p05l.th<^l.
,••-:;-•... •'■■■--V!*'; .- V'r:c}>-r;-->:-s;=>;>4.^.-:.?:vJ^ , v.; ,•
- Vi-'^^ ■/*•■ •^^■. /^ : : '■ •••r^^e-:^-^^^;^? ^^, - ■' . -nucl. pre
prerot.
3ubrot.
%-'V ' •"^ ■ ^'^i-!^ Mv rec ]&X. hyp.
nucl. dif. lob. I0.I.
108
107
313
/
PLATE 30
EXPLANATION OF FIGURES
109 Cells of the nucleus posterior thalami. Toluidin blue method. X 575.
110-113 Neurones of the nucleus posterior thalami. Golgi method. X 93.
From sagittal sections. As will be noted, the cells of this nucleus are very large.
They appear larger in sagittal than in transverse sections, both in toluidin blue
and Golgi material.
114 Transection at approximately the same level as that shown in fig. 106.
Weigert method. X 17.
com. horiz., commissura horizontalis; com. j^ofii., rommissura posterior; co»i.
trans., commissura transversa ;/a.sc. retr., fasciculus retroflexus; 7rucl. dij. lob. lot.,
nucleus diffusus lobi lateralis; nucl. -post, tub., nucleus posterior tuberis; micl.
prerot., nucleus prerotundus; nucl. rot., nucleus rotundus; nncl. subrot., nucleus
subrotundus; sac. vase, saccus vasculosus; tr. cbl. t'-.ci. + tr. rot. lent. + codi.
horiz., tractus cerebello-tectalis plus tractus rotundo-lentiformis plus commissura
horizontalis; tr. cbl. hyp., tractus cerebello-hypothalamicus; tr. olf. thai, vied.,
pars dors., tractus olfacto-thalamicus medialis, pars dorsalis; //'. nlf. thai, med.,
pars vent., tractus olfacto-thalamicus medialis, pars ventralis; tr. rot. lob., tractus
rotundo-Iobaris; tr. thai, 'mam., tractus thalamo-mammillaris; tr. thai, sp., tractus
t liiilaino-spinalis (Ka])pers).
314
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 30
114
■'vsm^
e?WB
tr. cbl. tect+tf. i-ot. lent.+ com. horiz
com. po5t.
f<^3c. -retr.
U'. tha.1. sp.
com. tvd.n5.
l-K \h^\. m^^'m.
nucl. prerot.
t-f. cbl. hyp.
nucl. rot.
com, hofiz.
t-ir: olf. th6.1. med., pexr3 vent
tr. olf. \h.&\. med., pe^vs dors.
nucl. subrot.
■tr. rot. lob.
|;VlUci. post. tub.
?hucl. dif. lob. la,t.
5&.C. Vc!s.5C.
315
PLATE 31
EXPLAXATIOX OF FIGURES
115 Transection slightly caudal to the level shown in fig. 114. Weigert method.
X 17.
116 Transection slightly caudal to the level shown in fig. 115. Weigert method.
X 17.
com. horiz. + tr. rot. lent., commissura horizontalis plus tractus rotundolentiformis; com. trans., commissura transversa; corp. mam. (G), corpus mammillare, the ganglion mammillare of Goldstein; fasc. retr., fasciculus retroflexus;
nucl. dif. lob. lat.. nucleus diffusus lobi lateralis; nucl. post, thai., nucleus posterior
thalami; nucl. pust. tub., nucleus posterior tuberis; nucl. prerot., nucleus prerotundus;nuc/. rut., nucleus rotundus; nucl. subrot., nucleus subrotundus; sac. vase,
saccus vasculosus; tr. cbl. tect., tractus cerebello-tectalis; tr. cbl. tect. + tr. rot.
lent. + co7n. horiz., tractus cerebello-tectalis plus tractus rotundo-lentiformis plus
commissura horizontalis; tr. cbl. hyp., tractus cerebello-hypothalamicus; tr. olf.
thai, med., pars, dors., tractus olfacto-thalamicus medialis, pars dorsalis; its connection with the nucleus subrotundus comes out with great clearness in these
figures; tr. olf. thai, med., pars, vent., tractus olfacto-thalamicus medialis, pars
ventralis; in fig. 116, immediately lateral to the nucleus rotundus, is shown the
termination of this fiarl; //•. ral. lab., tractus rotundo-lobaris; tr. thai, mam.,
tractus thalamo-mannnillaris; //•. thai, sp., tractus thalamo-spinalis (Kappers.)
316
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 31
'^^^^^^^W^^^^^jn^T'rrrrrtfs-^
tr. cbl. ieci\tr. rot.lent+com. horiz.
tr. tha.1. sp.
com. tr6.n3.
tr. tha.1. ma.m.
corn.honz.+ It' rol. lent.
nucl. post. th5,l.
nucl . prerot.
..tr olf. tha.1. med., pa.-r5 vent.
nucl. rot.
_ tr olf. tha.\. rried., p6>rs> dors.
Ltr rot. lob.
nucl. subrot.
nucl. post. tub.
bl. hyp.
dif lob.Kt.
Vc\5C.
.••>^;\yr:r.-j: . iiM l;;:v ■: ■' .ff^
Ir cbl. tect.
f<^5c. retf,
tr thavl. 5p.
ti-. olf. thb-l. ■med.,p6.f5 vent,
nucl. rot.
tr cbl. hyp.
tr olf .tha.!. Tned., ps^rs dors,
nucl. subrot.
tr rot. lob.
\Corp. ma^m. CG)
S&.C. V6.sc.
dif, Job. l6.t
317
PLATE 32
EXPLANATION OF FIGURES
117 Transection through the corpus mammillare, the ganglion mammillare of
Goldstein. Toluidin blue method. X 46.
118 Cells of the corpus mammillare. Toluidin blue method. X 575.
119-121 Neurones of the corpus mammillare. Golgi method. X 93. From
sagittal sections. It will be noted from figs. 117 to 121 that the cells of the corpus
mammillare are very small and closely packed.
corp. mam. (G), corpus mammillare, the ganglion mammillare of Goldstein;
nud. cbl. hyp., nucleus cerebellaris hypothalami; nucl. dif. lob. Int., nucleus
difTusus lobi lateralis; nucl. fasc. long., nucleus fasciculus longitudinalis medialis;
nucl. post, thai., nucleus posterior thalami; nucl. prcrot., nucleus prerotundus;
nucl. rot., nucleus rotundus; nucl. rub. (G), nucleus ruber of Goldstein; nucl.
subrol., nucleus subrotundus; s. mam., sulcus mammillaris of Goldstein; tr. chl.
led., tractus cerebello-tectalis.
318
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 32
-' ■M}^i^yMk. '
■ "■y".'••-.V^* ^■■
prerot.
i^nucl. vol.
nuql.post.lh6.L
cl. sub-fot.
118
120
319
PLATE 33
EXPLANATION OF FIGURES
122 Transection through the corpus mamminare. ^yeigert method. X 17.
123 Diagram showing the two parts of the right olfactory nerve, and the relations of their fibers to the cells of the bulb and to the fibers of the olfactory tract.
124 Diagram of a horizontal projection of the right olfactory bulb showing the
connections, in the bulb, of the different tracts of the crura.
Corp. mam. (G), corpus mammillare (of Goldstein) ; /«sc. rctr., fasciculus
retroflexus ;./('/. ulf., filaolfactoria; g.n.term., ganglion cell of the nervusterminalis;
gran, cell, granule cell of the nucleus olfactorius anterior; mitr. cell, mitral cell;
nucl. cbl. hyp., nucleus cerebellaris hypothalami; nucl. dif. lob. Ud.. nucleus diffusus lobi lateralis; n. olf. ant., nucleus olfactorius anterior; n. olf. lat., nervus olfactorius lateralis, consisting largely of fibers from the lamellae of the caudal and
lateral portion of the olfactory capsule; n. olf. med., nervus olfactorius medialis,
formed largely from fibers originating chiefly in the rostral and medial portion of
the capsule ; ?i. term. , nervusterminalis ; nucl. prerut., nucleus prerotundus ; n ucl. rot.,
nucleus rotundus ; nucl. subrot., nucleus subrotundus ; s. mam., sulcus mammillaris ;
tr. cbl. tect., tractus cerebello-tectalis; ir. olf. a.s'c., tractus olfactorius ascendens,
composed of centrifugal fibers from the corpus precommissurale, pars medianus;
ir. olf. asc, pars lat., tractus olfactorius ascendens pars lateralis; tr. olf.
a.s'c, /;c/r.s med., tractus olfactorius ascendens, pars medialis; tr. olf. lat., tractus olfactorius lateralis, composed of the following three tracts, all centripetal, and practically all terminating, in the carp, in the nucleus olfactorius
dorsalis and nucleus pyriformis of the same side; tr. olf. lat., pars, inter med., tractus olfactorius lateralis, pars intermedia; //■. olf. lat., pars lat., tractus olfactorius
lateralis, pars lateralis; tr. olf. lat., pars med., tractus olfactorius lateralis, pars
medialis; //■. nlf. med., tractus olfactorius medialis, the mesal part of the medial
olfactory radix of authors, divided into the following; tr. olf. med., pars lat.,
tractus olfactorius medialis, pars lateralis, terminating, after decussation in the
anterior commissure, in the nucleus pyriformis of the opposite side; tr. olf. med.,
pars med., tractus olfactorius medialis, pars medialis, forming the commissura
interbulbaris of most authors which, as indicated in figs. 136 and 138, is largely
a decussation and not a commissure; ir. thai, sp., tractus thalamo-s])inalis
(Kappers).
320
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 33
^^:^
%>-_• -,, -_
tr. cbl tect.
f^-sc retr
t^ tha,l. 5p.
122
nucl. rot.
nucl. subfot,
nucl. cbl. "hyp.
Corp. mcym. CG)
nucl.dil lob. ]bX.
5.m2i.Tn.
n olf. med.
n. olf. la.1.
<§. n. term,
til. olf,
-grA-n, cell
n.olf e^nt.
mitr cell,
n. term,
tr. olf. med.
Ir. olf. 6.5 c.
tr olf. W{.
123
.■g. n. term.
-tr olf. la>.t., p6.r5 la.t.
,tr olf. lev-t., pei.r5 mtermed.
tr olf. la.t., p<^.r5 med.
,tr olf. a^5c., p<5.r5 lev.t.
,tr. olf. ei.5c, p6.r3 med.
.tr olf. med., pe^rs les^t.
tr. olf. med.,p6.r5 med.
.n. term.
.tr olf. lAt.
.tr olf. 5.5 c.
-tr olf. med. 124
321
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3
PLATE 34
EXPLANATION OF FIGURES
125 Diiigraiii i)f :i projection of the olfactory centers on a parasagittal plane,
near the meson, showing the levels at which figs. 127 and 128 are taken and the
relation of the different centers to the four primitive columns. X 11.
1, pars dorso-medialis hemisjihaerii and epithalamus; 2, pars dorso-latcralis
hemisphaerii and pars dorsalis thalami; 3, pars ventro-lateralis hemisphaerii and
pars ventralis thalami; 4, pars ventro-medialis hemisphaerii and hypothalamus;
tr. olf. lat., tractus olfactorius lateralis; tr. olf. med., tractus olfactorius medialis.
(For other abbreviations see explanation of fig. 141.)
322
OLFACTORY CENTERS IN TKLEOSTS
RALPH EDWARD KHKLDOiN
PLATE 34
lO
C\J
323
PLATE 35
EXPLANATION OF FIGURES
126 Diagram of a transection through the hemispheres of an embryonic teleost,
showing the rehitions of the four primitive columns.
127 Diagram of a transection through the hemispheres of an achilt teleost,
showing the changes which have taken place through rearrangement of these
columns. For approximate level see fig. 125.
128 Diagram of a transection through the diencephalon of an cmbrj'onic teleost, showing the relations of the same columns. Practically the same conditions
hold in the adult. (For level see fig. 125.)
129-134 Diagrams of transections through the cerebral hemispheres of Amoiurus, at the level of the anterior commissure, showing the shifting which takes j)lace
with the gradual eversion of the tenia. Figs. 129 to 133 are camera lucida drawings
obtained through the kindness of Dr. James M. Wilson, of Washington, D. C.
Fig. 129, 5 mm. stage; fig. 130, 6 mm. stage; fig. 131, 9 mm. stage; fig. 132, 10 mm.
stage; fig. 133, 12-13 mm. stage; fig. 134, adult.
135 Transection through the cerebral hemispheres of Amia calva in the region
of the anterior commissure, to illustrate the eversion of the hemisphere wall,
after Mrs. Susanna Phelps Gage ('93).
/, pars dorso-medialis hemisphaerii and epithalamus; 2, pars dorso-lateralis
hemisphaerii and pars dorsalis thalami; 3, pars ventro-lateralis hemisphaerii
and pars ventralis thalami; 4, pars ventro-medialis hemisphaerii and hypothalamus; f/^yV/m/., epithalamus; hypolhal., hypothalamus; pars dors, thai., pars
dorsalis thalami; parn vent, thai., pars ventralis thalami; .s. /////. tcL, sulcus
limitans telencei)hali; .s///r. ilicri. dor.s. sulcus diencephalicus dorsalis; .swif. (/icn.
med., sulcus diencpphalicus medialis; .su/c. dien. vent., sulcus diencephalicus
ventralis.
324
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 35
325
PLATE 36
EXPLANATION OF FIGURES
136 Diagram of a horizontal projection of the olfactory centers showing in
blue the connections of the corpus precommissurale, together with the fiber components of the fasciculus medialis hemisphaerii and associated tracts. X 12.
bulb, olf., bulbus olfactorius; c. mam., corpus mammillare, ganglion mammillare of Goldstein; cor p. precom., corpus precommissurale, consisting of the pars
medianus, pars commissuralis, and pars supracommissuralis; ci'us olf., crus
olfactorium; ent., nucleus entopeduncularis; fib. precom. str., fibrae precommissurales striatici, running from the precommissural body to the palaeostriatum;
hab., ganglion habenulae; hyp., hypophysis; m., pars magnocellularis of the nucleus preopticus; n. ant. tub., nucleus anterior tuberis; n. cbl. /ij/p., nucleus cerebellaris hypothalami of Goldstein; n.c.l., nucleus commissuralis lateralis ; n.
dif. lob. Int., nucleus diffususlobi lateralis; n. int., nucleus intermedius ; n. lat. tub.,
nucleus lateralis tuberis; ?;. olf. lat., nucleus olfactorius lateralis; n. posthab.,
nucleus posthabenularis; n. post, thai., nucleus posterioi- thalami of Goldstein;
n. post, tub., nucleus posterior tuberis; n. preopt., nucleus preopticus; n. prerot.,
nucleus prerotundus; n. pyr., nucleus pyriformis; n. rot., nucleus rotundus; n.
sw/6/-., nucleus subrotundus; n. ten., nucleus teniae; n. tertn., nervus terminalis;
p. a., i)ars parvocellularis anterior of the nucleus preopticus ; paleostr., palaeostriatum, the striatum of most authoi-s; pars, com., pars commissuralis of the corpus
precommissurale; pans, med., pars medianus or the nucleus medianus of the corpus
precommissurale; p.p., pars parvocellularis posterior of the nucleus preopticus; p.
sup. com., pars supracommissuralis of the corpus precommissurale; sac. vase, saccus vasculosus; <e^a, the so-called pallium ; //■. Injp. olf. mvd., tractushyi)othalamoolfactorius medialis; ir. med. preopt., pars aid., tractus mediano-preopticus, pars
anterior; fr. med. preopt.. pars post., tractus mediano-preopticus, pars posterior;
/r. o//. asc. , tractus olfactorius ascondens;/r. o//. asc., pars lat., tractus olfactorius
ascendens. pars lateralis; //•. nlf. asc, j)ars mciL, tractus olfactorius ascendens,
))ars medialis; tr. olf., med., pars tat., tractus olfactorius medialis, pars lateralis;
tr. olf. med., pars, med., tractus olfactorius medialis, jiars medialis;//'. olf. thai, med.,
pars dors., tractus olfacto-thalamicus medialis, pars dorsalis; tr. olf. thai, med.,
pars intermed., tractus olfacto-thalamicus medialis, pars intermedia (short descf 1 1 ding association fibers) ; //•. olf. thai . ni< d . fiar-s /v///., t r;icl us olfaito-t hal amicus
metUalis, pars vent ralis; /;•. opt., trad us opticus; //■. //no /j/. /»/)., tr:ict us pi'copt.icotuberis; //■. Ihal. olf. nnd., j>ins I nlcniicd., tr;iclus tli;il;iin()-()lf:icf oiiiis iiic(li;ilis,
pars intermedia (siioit ascending association libers).
32(i
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE :5fi
tr olf. a,5c., pe^r5 Icvt.
tr olf. 6>5c., pa.rs. med
t-r olf. med., pe^rs med.
n. term.
tY. olf. med.^pcxrs. lat.
olf. ASC.
b. p^^ecom. stir"
med. preopt.^ pdxTS &nt.
olf. th£)«l. med.^ p<^vs vent,
ti-. olf. Vr\&]. Tned., pa.fs doi-a.
hyp, olf. med.
. med. preopt._, ^(^.v^ post.
preopt tu.b.
olf. theiLl med.. pars intermed
thaV olf. med.,pe\r5 mtenned.
136
PLATE 37
EXPLANATION OF FIGURES
137 Diagram of a horizontal projection of the olfactory centers showing the
connections of the nucleus pyriformis, nucleus teniae, nucleus olfactorius lateralis, and nucleus intermedius. On the right side are shown the tracts terminating in these nuclei, on the left side the tracts originating in them. X 12.
com. hab. (red), com. habenularum; tr. entoped. intermcd. (red), tractus entopedunculo-intermedius; //•. hijp. olf. led. (blue), tractus hypothalamo-olfactorius
lateralis; tr. inlermed. cnluped. (red), tractus intermedio-entopeduncularis; tr.
intermed. hab., pars ant. (red), tractus intermedio-habenularis, pars anterior; tr.
intermed. hah., pars post, (red), tractus intermedio-habenularis, pars posterior;
tr. intermed. posthah. (blue), tractus intermedio-posthabenularis; Ir. intermed.
preopt. pars ant. (red), tractus intermedio-precopticus, pars anterior; tr. intermid, preopt., pars med. (red), tractus intermedio-i)reopticus, pars medialis; tr.
olf. hyp. lat. (blue), tractus olfacto-hypothalamicus lateralis; tr. olf. lat. (blue),
tractus olfactorius lateralis; //■. olf. lot., jxirs iulenncd. (blue), tractus olfactorius
lateralis, pars intermedia; //■. olf. lot., pars incd. (l^luc), tractus olfactorius lateralis, pars medialis; tr. olf. tned., pars lat. (blue), tractus olfactorius medialis, pars
lateralis; tr. posthah. intermed. (blue), tractus posthabenulo-intermedius; ir.
praeth. cin. (blue), tractus praethalamo-cinereus; /r. preopt. intermed., pars ant.
(red), tractus preoptico-intermedius, pars anterior; //■. i)ri'iipt. inlenned., jxirs
lat. (red), tractus preoptico-intermedius, pars lateralis; tr. preopt. intermed.,
pars med. (red), tractus preoptico-intermedius, pars medialis; tr. ten. (red), tractus teniae, the tractus olfacto-habenularis of KapjxM-s, ( loldslciii, etc. (For
other abbreviations see explanation of fig. 136.)
328
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
tr. o\f. lat.pftTS \dX
ir oJf. la.t.,pM'3 intermed.
ir. olf 1 At., para med
tr olf. medLjP^ra IbX.
t+- olf ]dX..
ten
^intermedpreopt.^ pA^^S) a^nt.
tf^phtefmed hab., p^^s d.nt.
t*^i 517 termed, preopt., pev^"6 med.
W ihtermed entoped.
tv. intermed . pozthdh.
ttrmtermed. h^b.^pd^^s post,
.tirpra^eth. cm.
tr pKeopt. intenned.,p6irs med.
preopt. intevmed.jpAKs dvnt.
tt: entoped. jntermed.
tr preopt. mtermed., pa.vis l^t.
com. hab.
vt+: posthab. mterrned.
tK hyp. olf. Kt.
olf. hyp. lat.
137
329
PLATE 3 two nuclei olfactoi'ii ilorsales or
l)riinordia hippocampi; ro///. hi pp., pars post, (green), commissura hippocampi,
pars [)osterior, the commissura internuclearis of Goldstein; com. interbiilb., (dec.
tr. olf. med., par.<i med.) (blue), commissura interbulbaris (decussation of the
tractus olfactorii mediales, partes mediales) ;co//(. nucl. preopt. (green), commissura nucleorum preopticorum; dec. ii. Icnii. (blue), decussatio nervorum terminalium; dec. tr. olf. nicd., pors lal. (blue), decussation of the tractus olfactorii
mediales, partes laterales; gang. n. term, (blue), ganglion cell of the nervus
terminalis; n. term, (blue), nervus terminalis; tr. hyp. olf. med. (red), tractus
hypothalamo-olfactoriusmedialis;ir. olf. med. (blue), tractus olf actoriusmedialis;
tr. olf. med., pars lat. (blue), tractus olfactorius medialis, pars lateralis; tr. olf.
med. pars med. (blue), tractus olfactorius medialis, pars medialis; tr. strio-thal.
cruc. (red), tractus strio-thalamicus cruciatus (shown only on one side); tr.
thai. str. crw. (red), tractus thalamo-striaticus cruciatus, (shown only ononeside).
(I'^or olhcr abbreviations sec ('\i)ianation of fig. 136.)
330
OLFACTORY CENTERS IN TELECASTS
RALPH EDWAHD SHELDON
w
^ang. n. tevm.
n. lerm
tr. olf. med., p6.r5 med.
.tr. olf. med., pav-rs l<2>.t.
t*^ olf. med.
com , Corp. pre com.
dec. n. term.
com. hipp., p^rs Ant.
corn. interbulb.^Cdec. tr olf. med.
pevrs med.;
com. dors,
tr. hyp. olf. med.
com.hipp.^pdvrs post,
dec. tr olf. med., pd^rs lat.
tr. strio-thA.1. c-ruc.
tr: theJ. 3tr cr uc.
com. nucl preopt.
138
331
PLATE 39
EXPLANATION OF FIGURES
139 Diagram of a horizontal projection of the olfactory centers showing
in blue the pathways of the fibers entering into the composition of the fasciculus lateralis hemisphaerii. The ascending fibers are shown on the right, the
descending on the left. X 12.
fib. precom. str., librae precommissurales striatici; //•. ulf. hyp. lai., tractus
olfacto-hypothalamicus lateralis; tr. strio-thnl. cruc, tractus strio-thalamicus
cruciatus; tr. .Ktrid-lhal. iiirruc, tractus strio-thahimicus incniciatus; tr. thai. str.
cruc, tractus thalanio-striat icus cruciatus; tr. thai. .s/r. inrrur.. tractus-thalamostriaticus incruciatus. (I'or otlici' abl)rcviati()ns see (>x|)lanation of fig. 136.)
332
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 39
fib. pre com. stt^
tr. th&l. str. cru.c.
tf. 3ti-io-lhAl. cr\JiC.
t-r. strio-tywl. incfoic.
tr. thai, str inci-uc.
tr oil hyp. Idt.
139
.*?.33
PLATE 40
EXPLANATION OF FIGURES
140 Diagram of a horizontal projection of the olfactory centers showing the
connections of the postcommissural olfactory nuclei, with the exception of the
habenular fibers shown on fig. 142. Fibers which terminate in these centers are
shown on the right, while those which originate from them appear on the left.
X 12.
co))r. nucl. preopt. (red), commissura nucleorum precpticorum; tr. entoped.
preupt. (red), tractus entopedunculo-preopticus; ir. intermed. preopt., pars ant.
(red), tractus intermedio-preopticus, pars anterior; tr. intermed. preopt., pars vied.
(red), tractus intermedio-preopticus, pars medialis; tr. Int. preopt. (red), tractus
lateralis preopticus; ^r. med. preopt., pars ant. (blue), tractus mediano-preopticus,
pars anterior; tr. med. preopt., pars post, (blue), tractus mediano-preopticus, pars
posterior; tr. olf. med., pars lat. (blue), tractus olfactorius medialis, pars lateralis
(see fig. 136); tr. posthab. preopt. (red), tractus posthabenulo-preopticus; tr.
praeih. cin. (blue), tractus praethalamo-cinereus; tr. preopt. entoped. (red),
tractus preoptico-entopeduncularis; tr. preopt. intermed., pars ant. (red), tractus
preoptico-intermedius, pars anterior; tr. preopt. intermed., pars lat. (red), tractus
I)re;)ptico-intermedius, pars lateralis;//', preopt. intermed., pars med. (red), tractus
preoptico-intermedius, pars medialis; tr. preopt. lot. (red), tractus preopticolateralis; tr. preopt. posihah. pars ant. (red) tractus preoptico-posthabenularis,
pars anterior; tr. preopt. piixlliali.. jxirs post, (red), tractus preoptico-posthabenularis, pars posterior; tr. preopt. till), (blue), traclus prco]>tico-tuber;s. (For
other abbreviations see explanation of fig. 136.)
334
OLFACTOUV CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 40
tr olf. med., pck^s la,t.
tr. med. pt-eopt.^ pev-rs a^nt.
if. preopt, intenm.ed.,p&r5 ^nt.
tr. preopt. l&t.
com. nucl. pre opt.
tr. intermed. preopt., pa.rs atiI.
tv: Idt. preopt.
tr. intei-med. pfeopt., p^kTs med.
tr preopt. mtermed., p^rs med.
tr preopt. entoped.
tr entoped. preopt.
tr. preopt. intermed., pArs \^t.
140
tr. preopt. posfh&b., p6.r5 "post.
vtr posthab. preopt.
tr preopt. po5the>.b., pars ant.
tr pr5,eth. cin.
tt: preopt. tub.
PLATE 41
EXPLANATION OF FIGURES
141 Diagram of a projection of the olfactory centers on a para-sagittal plane
near the meson, showing the components of the tractus olfacto-habenularis, and
their connections, in black (cf. Gohhtehi, Taf. 11, Jig. 7). X 12.
chias., optic chiasma; com. cor p. jnccom. + com. hi pp. pars ant., commissura
corporium precommissnralium plus commissura hippocampi, pars anterior; com.
hub., commissura habenularum; com. Hcrrick, commissura Herricki; com. horiz.,
commissura horizontalis; co)n. interbulb. {dec. tr. olf. nicd., pars vied.) commissura
interbulbaris (decussation of the tractus olfactorii mediales, partes mediales) ; ccm.
nucl. preopt., commissura nucleorum preopticorum; cow. trans., commissura transversa; corp. mam., corpus mammillare; corp. pin., corpus pineale; corp. precom.,
corpus precommissurale; crus olf., crus olfactorium; dec n. term., decussatio
nervorum terminalium; dec. ir. hyp. olf. med. + dec. tr. idf. mcd.. pars hit. + com.
dors. + com. hi pp., pars post., decussation of the tractus hypothalamo-olfactorii
mediales, plus decussation of the tractus olfactorii mediales, partes laterales, plus
commissura dorsalis, plus commissura hippocampi, pars posterior ;/«sc. retr., fusciculusretroflexus;yi6.r;«.s., fibraeansulatae; hub., ganglion habenulae; n. ant. tub.,
nucleus anterior tuberis; //. opt., nervus opticus; n. post. tut).. luicleus posterior
tuberis; nucl. dif. lob. lot., nucleus diffusus lobi lateralis; nucl. posthab., nucleus
posthabenularis; uucl. preopt., nucleus preoptions; nncl. rot., nucleus rotundus;
pars gland., pars glandularis of the hypophysis; pars med., pars medialis of the
corpus precommissurale; pars ncrr., i)ars nervosa of the hypophysis; j)ars p.c.
post., pars parvocellularis posterior of the nucleus preopticus; p.m., pars magnocellularis of the nucleus preopticus; p. p. c. ant., pars parvocellularis anterior of
the nucleus preopticus; /;. supraeom., pars supracommissuralis of the corpus precommissurale; tectum, tectum mesencephali; tela, so-called ])allium; tr. die?), hab.,
tractus diencephalo-habenularis; tr. entoped. hab., tractus entopeduncuio-habenularis; tr. hab. dien., tractus habenulo-dienccphalicus; //■. iutermed. hati.. jxirsant.,
tractus intcrmedio-habenularis, pars anterior; //•. i)it<rm((i. halt., i)(irs post., tractus intermedio-hab(>nularis, pars posterior; //•. olf. hnl).. I met us olfacto-habenularis; //•. jiost/iab. hob., t ractus postliabciiulo-habcnularis ; //■. prcojil. fiiib., iiars
ant., tractus preoi)tico-habenularis, pars anterior; //■. pnopl. hat)., pars lot.,
tractus preoptico-habenularis, i)ars ItitovuMs; Ir. jircoj)! h<il>., pars mcd., tractus
preopt ico-habciudaris, pars medialis ; //•. prcopl . halt., /xrrs post., tractus preopticohabenularis, j)ars posterior; //•. .s//-/o-//(r//. r///r., decussation of the tractus striothalamici cruci.ati; tr. teniae, tractus teniae; calvula, valvula cerebclli. (See
also fig. 125. J
336
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 41
337
THE JOURNAL OF COMPARATIVE NEUROLOOY, VOL. 22, NO. 3
PLATE 42
EXPLANATION OF FIGURES
142 Diagram o' a liorizoiital iiiojectiou of the olfactory contors showing, in
red, the components of the tractus olfacto-habenularis and their connections.
X 12.
cum. hab., commissura habenuhirum, or commissura siii)erior; fasc. relr.,
fasciculus retrofiexus, Meynert's bundle, tractus liabenulo-peduncularis; tr.
(lien, hab., tractus dienccphalo-habenularis (a portion of the tractus habenulodiencephalicusof Goldstein) ; tr. entoped. /i«6., tractus entopedunculo-habenularis;
tr. hah. dien., tractus habenulo-diencephalicus; tr. intermed. hah., pars, ant.,
tractus intermedio-habenularis, pars anterior; tr. intermed. hah., pars j)ost.,
tractus intermedio-habenularis, pars posterior; /;•. olf. hab., tractus olfactohabenularis (under this name are included all the fiber systems which ascend
into the habenula of either side); tr. posthah. hab., tractus posthabenulohabenularis; tr. preopt. hab., pars ant., tractus preoptico-habenularis, pars
anterior; tr. preopt. hab., pars lat., tractus preoptico-habenularis, pars lateralis;
tr. preopt. hab., parsmed., tractus preoptico-habenularis, par medialis; tr. preopt.
hab., pars post., tractus preoptico-habenularis, pars posterior; tr. ten., tractus
teniae (the tractus olfacto-habenularis of Kappers, (Joldstein, etc.). (For other
abbr(!V'iations see (!\plan;itioii of fig. V.iC).)
338
OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON
PLATE 42
Ir. intermed. hev.b., pe^rs &nt.
ir. preopt. ha^b.^ p&rs Ant.
tt: ten.
tK entoped. he^b.
t-i' preopt. hab.^p&rs med.
t^. mtermed. hbb., pe^rs post.
tf. olf. hAb.
tr preopt. h^b., p&rs post.
com. hab.
tr. preopt. hajD.,p6.r3 la.t.
tr. posth^b. hevb.
fAsc. fetv.
\r. dien. hdb.
tr hab. d^en.
142
339
THE TELENCEPHALON IN CYCLOSTOMES^
J. B. JOHNSTON
From The Institute of Anatomy, University of Minnesota
FORTY-ONE FIGURES
The telencephalon of cyclostomes presents in many ways more
primitive conditions than are known in other vertebrates. Cyclostomes are therfore important in the effort to trace the phylogeny
of various structures in the cerebral hemispheres. The discussions
regarding the interpretation of the lateral lobes, the pallium and
the ventricles (Ahlborn, Rabl-Riickhard, Studnicka, Edinger)
together with the contributions by Sterzi ('09) and the writer
('02a), have made clear the significance of most parts of the telencephalon at least in Petromyzonts. The lateral lobes are true
hemispheres,- containing lateral ventricles connected with the
third ventricle by wide interventricular foramina. The hemispheres are pushed back against the sides of the diencephalon by
pressure from the buccal apparatus. The bulbar formation occupies the broad rostral wall of the hemisphere and does not project
forward as a bulbus olfactorius. In addition to this bulbar formation the hemisphere walls include secondary olfactory centers
and a basal-central area heretofore known as corpus striatum.
The bulbar formation and secondary olfactory centers are separated by a groove which represents the olfactory peduncle.
The anterior portion of the third ventricle is closed above and
rostrally by a membrane which is thickened in two places by
commissures (figs. 5. 6). Rostral to the extraordinarily thick
1 Neurological Studies from the Institute of Anatomy, Universitj' of Minnesota,
No. 16.
- The writer here uses the term hemisphere as synonjauous with the lateral lobe
or evagination of the telencephalon, accepting in this the suggestion of Professor
Herrick ('10, p. 492).
341
THE JOURNAL OF t CMPARATIVE NEUROLOGY. VOL. 22, XO. 4
AUGUST, 1912
342 J. B. JOHNSTON
chiasma ridge the lamina terminalis extends from the preoptic
recess to the recessus neuroporicus, rostral to the interventricular
foramen. The position of the recessus neuroporicus was first
clearly established by Sterzi ('07). The lamina terminalis is
thickened by the anterior commissure. Above the recessus neuroporicus the roof of the ventricle is thickened by the so-called
dorsal olfactory commissure or decussation. This thickened
lamina should be called the lamina supraneuroporica (Burckhardt '94 b, '94 c, '07, Johnston, 'lib). A short distance caudal
to this lamina occurs a small fold in the membranous roof which
was shown by Sterzi ('07) to be the velum transversum. Caudal
to this a long dorsal sac extends to the superior commissure and
habenular bodies. This dorsal sac is covered dorsally by the
parapineal body and epiphysis, which depress the sac in various
degrees.
Upon the general morphology of the petromyzont telencephalon
thus far there is general agreement among workers. There are,
however, disputed questions regarding the relations of the telencephalon and diencephalon, and the location of the primordium
of the cortical area of higher vertebrates.
The writer has reviewed the preparations previously studied
and has examined new preparations of the same and other species
of petromyzonts. The writer wishes to express his sincere thanks
to Professor Gage for a very generous supply of ammocoetes and
adults of both Lampetra and Petromyzon dorsatus. Other specimens of Lampetra have been obtained from Professor Reighard's
laboratory both while the writer was located there and later
through the kind assistance of Dr. L. J. Cole. The writer is
deeply indebted to Professor Charles Brookover for the loan of
the series of sections of Ichthyomyzon which is described beyond.
Thanks are also due to Professor Reighard for the loan of a series
of sections of a new dwarf lamprey not yet described. Through
the kindness of Mr. W. F. Allen of this laboratory I have had the
opportunity to section and study several stages of the ammocoetes
of the Pacific coast lamprey, Entosphenus.
THE TELENCEPHALON IN CYCLOSTOMES 343
The di-telencephalic boundary
The writer has attempted ('09) an accurate definition of the
boundary in question, upon the basis of selachian, amphibian,
avian and mammalian embryos. The result was to show that
the optic chiasma belongs to the telencephalon, the boundary
being defined by the velum trans versum above and the caudal
surface of the chiasma ridge below. It was shown that the telencephalon includes, in addition to the hemispheres, a median portion surrounding the rostral part of the third ventricle. The
floor of this telencephalon medium is occupied by the optic
chiasma. Its roof (roof plate of His) is made up of the lamina
terminalis, lamina supraneuroporica and tela chorioidea. The
telencephalon constitutes a complete brain ring or segment as
His contended, although shorter than His thought. The hemispheres are lateral evaginations of this telencephalon medium. In
the series of vertebrates, as in the stages of the ontogeny, a progressively larger part of the telencephalon is evaginated into the
hemispheres, until in man only the chiasma ridge and the small
region between it and the lamina terminalis remains as the telencephalon medium.
This definition of the di-telencephalic boundary has been
accepted by Herrick ('10), Kappers and Carpenter ('11), and others,
and its substantial correctness will be assumed for the purposes
of this paper. If the di-telencephalic boundary is to be determined in cyclostomes in the same way as in other vertebrates,
it becomes necessary only to describe the velum transversum in
cyclostomes accurately and completely, since the chiasma ridge
is already well understood.
The recognition by Sterzi of the small fold behind the dorsal
decussation as the homologue of the velum transversum of higher
forms was a valuable contribution to the interpretation of the
cyclostome brain. The velum was recognized, however, only in
median sections and the postition of the velum in the median
plane does not define the boundary between the telencephalon and
diencephalon. The writer has shown at length elsewhere ('11 a,
'lib) the errors and inconsistencies which arise from taking into
account only the. position of the velum in the median plane. It
344 J. B. JOHNSTON
is the point of attachment of the vekim to the massive walls which
determines the boundary between telencephalon and diencephalon.
The velum transversum is a fold of the tela chorioidea having the
form of an arch whose pillars rest on the massive lateral walls.
This point of attachment is the meeting place of the taenia thalami
and taenia fornicis. The position of the velar arch in the median
plane depends upon the form of the tela chorioidea of the third
ventricle as affected by the general form of the brain and the
pressure or traction exerted upon the tela by surrounding structures. Thus in the selachian brain the velum is nearly transverse
and vertical in position (fig. 1) and is attached to the lateral walls
just in front of the habenular bodies. In certain ganoids, on the
other hand, the velum is a very deep fold which is inclined forward at an angle greater than 45 degrees. The pillars of the
velum are attached to the lateral walls just rostral to the habenular bodies exactly as in selachians (fig. 2). The point of attachment of the velum to the lateral walls may be more sharply defined
with reference to the internal structure of the massive wall. It
is just at the point of attachment of the velum that the several
categories of fibers which make up the stria medullaris converge
into a compact bundle to ascend to the habenular nucleus and
commissure (commissura superior Osborn). In amphibians and
reptiles this portion of the lateral wall, to which the velum is
attached and which is traversed by the stria medullaris, Herrick
('10, p. 419) has called the eminentia thalami. This low eminence
is clearly seen in figures 1 and 2, but is not lettered.
A careful study of the velum transversum in Lampetra shows
that it is attached as in fishes and amphibians immediately rostral
to the habenular bodies and that its point of attachment is the
dorsal border of the eminentia thalami.
As is well known, the right habenular body is very much larger
than the left, and each is bounded ventrally by a deep groove, the
sub-habenular sulcus (figs 3, 5, 6). At its rostral end this deep
sulcus leads into the dorsal sac. Here it meets with a vertical
sulcus which descends in the brain wall and curves forward to
enter the interventricular foramen (figs. 5, 6, sulcus limitans hippocampi). The common space formed by the union of these two
THE TELENCEPHALON IN CYCLOSTOMES 345
deep sulci where they join in the caudal and lateral angle of the
dorsal sac is a very deep and narrow cleft which may be called
the recessus praehabenularis (figs. 14, 18). This deep recess has
been formed probably by the crowding together of the brain due
to pressure from in front. Below the habenular body two nearly
vertical ridges are seen (figs. 5, 6) in the side wall of the thalamus.
The more caudal one is occupied by the tractus habenulo-peduncularis (figs. 21, 22). It is much more prominent on the right,
owing to the greater size of the nucleus habenulae and the fiber
tract on the right side. The more cephalic ridge is about equally
developed on the two sides and contains the stria medullaris (figs.
20, 21). This I shall call the eminentia thalami. It is bounded
in front by the sulcus limitans hippocampi and extends up in the
recessus praehabenularis as a narrow ridge (figs. 20, 26, 27). The
groove separating the two ridges corresponds to the sulcus b of
the selachian brain (Johnston '11a) and to the sulcus diencephalicus medius of Herrick ('10) in amphibians.
The dorsal ridge in front of the habenular body is large in
Lampetra and presents a slight but distinct eversion similar to
that in the teleost brain (figs, 7, 30, 31). To this ridge the writer
formerly ('02 a) gave the name epistriatum. In anticipation of
the results of the following pages, we may call it here the primordium hippocampi. It extends forward over the interventricular
foramen where it becomes continuous with the roof of the lateral
evagination.
In order to determine whether this ridge belongs to the telencephalon or diencephalon we must discover the point of attachment of the velum transversum to the massive walls. This point
is difficult to determine in most petromyzonts because the velum
is very rudimentary and is recognizable only near the median line.
This is true of the adults of Petromyzon dorsatus and Lampetra
which the writer has examined, of Ichthyomyzon studied by Herrick
and apparently of the forms studied by European authors. In
the ammocoetes of Petromyzon dorsatus, however, the velum is
better developed and appears as a fold which extends across the
whole width of the tela so that the attachment to the massive
walls can be determined.
346 J. B. JOHNSTON
In order to demonstrate the pillars of the velar arch in this
form the writer has made a plate reconstruction of the dorsal
part of the telencephalon and diencephalon. Owing to the compression of the dorsal sac by the epiphysis and parapineal body the
velum shows to best advantage in sagittal sections and the reconstruction was made from these (fig. 8). The model was made
from the left side of the brain and included the recessus neuroporicus in front and a part of the nucleus habenulae behind. In
order to see as much of the velum as possible the model has been
drawn from a medio-ventro-caudal direction. This figure should
be compared with figure 3, which shows the left half of the forebrain from a model of another specimen of Petromyzon dorsatus
(ammocoetes). The cut surface along the upper border of the
figure corresponds very nearly to the median sagittal plane. In
this plane is seen the fold described by Sterzi as the velum transversum. Extending caudo-laterally from this above the primordium hippocampi is a fold of the tela which continues without
interruption into the extreme caudo-lateral angle of the dorsal
portion of the ventricle. The deep cleft in which the velum is
seen in the figure is the recessus praehabenularis described above.
In the depth of this recess the lateral pillar of the velar arch is
attached to a small ridge which is identified as the eminentia
thalami by the presence in it of the stria medullaris. As the
model is viewed from an unusual angle, the relations will perhaps
be more cleai- by comparison with figures 23 to 27, which represent
five sections of the series from which the model was constructed.
The relations of the recessus praehabenularis and of the eminentia
thalami in Lampetra are shown in figures 14 to 22. Here the
sulcus praehabenularis is narrower than in the ammocoetes
because of the enlargement and crowding of the surrounding parts.
The disposition of the velum transversum in Petromyzon dorsatus
is essentially the same as that in ganoids and teleosts. The
velum is not only inclined far forward as in the latter fishes, but
owing to the dei)rossion of the dorsal sac by the overlying epiphysis, its middle part is pressed down far below the plane of attachment of its pillars. The whole course of the velum is diagrammatically represented in figure 28 as it might be seen in the dorsal
THE TELENCEPHALON IN CYCLOSTOMES 347
aspect of the brain. As indicated in this figure, that portion of
the dorsal ventricular space which lies above the velum transversum is properly called the dorsal sac, while the portion below the
velum belongs to the telencephalic portion of the third ventricle.
This description of the velum transversum makes it possible
to define clearly the boundary between the telencephalon and diencephalon. It is marked, as shown in figures 5 and 6, by a line
running from the attachment of the velum transversum upon the
dorso-rostral border of the eminentia thalami to the caudal surface
of the chiasma ridge.
The ventricular sulci in diencephalori and telencephalon
Attention has been called above to the sulcus limitans hippocampi, the dorsal or sub-habenular sulcus and the sulcus b or
sulcus medius. In figure 5 are to be seen three other important
ventricular grooves, the sulcus limitans of His, the sulcus hypothalamicus and a sulcus connecting the recessus praeopticus with
the foramen interventriculare. The presence of the last named in
embryos and adults of other classes of vertebrates has been pointed
out ('11 a). The further study of slightly evaginated brains
(cyclostomes, ganoids and teleosts) makes it necessary to withdraw the view stated earlier (in '11 a, p. 45) that the sulcus arising
in the preoptic recess is the continuation of the sulcus limitans
hippocampi.
The sulcus hypothalamicus is seen a short distance behind the
interventricular foramen diverging ventrally from the sulcus limitans hippocampi. It grows deeper and descends into the hypothalamus as a crescentic groove. Discussion of the question
whether this sulcus or any part of it is comparable to the sulcus
hypothalamicus of the human brain is reserved. The name is
used here in a purely descriptive sense and is evidently appropriate.
The sulcus is the same as Herrick's sulcus diencephalicus ventralis.
This name has not been adopted because the sulcus in all lower
vertebrates is a transverse rather than a longitudinal sulcus.
The sulcus limitans of His traverses the midbrain in the same
position as in other vertebrates and meets the sulcus hypothalamicus over and in front of the tuberculum posterius. It can not be
348 J. B. JOHNSTON
traced forward to the preoptic recess, apparen'tly owing to the
great prominence of the chiasma-ridge and the supra-optic nucleus.
Professor Herrick has given an account of the sulci in Ichthyomyzon which differs from the above account in important respects.
With Professor Herrick's kind permission I reproduce his figure
73 as figure 29 of this paper. Comparison of this with my figure
5 representing the model of the Lampetra forebrain shows that
Herrick has given the name sulcus diencephalicus medius to a
part of my sulcus hypothalamicus and that he has described the
lower end of this sulcus hypothalamicus as a separate sulcus under
the name of the sulcus diencephalicus ventralis. He recognizes
also a sulcus subhabenularis and sulcus diencephalicus dorsalis.
As it was impossible to harmonize this description with the
condition in Lampetra, I have secured for study at Professoi
Herrick's suggestion the identical series of sections from which
his drawings were made. The sections are fifteen microns thick
and with the exception of a single broken section the series is
perfect. A model has been made at a magnification of 100 diameters, the right half of which is drawn from the ventricular surface
in figure 6. The model when finished was a trifle longer than it
should be, in the proportion of 94 to 90.
Referring to Herrick's figures 74 to 81, it should be noted that
Professor Herrick viewed the sections from in front, so that the
right side of the brain appears in the left side of his figures. Thus
the right nucleus habenulae, which is the larger, appears on the
left side in figures 80 and 81. From this it follows that the reconstruction in figure 73 (figure 29 of this paper) represents the
ventricular surface of the right half of the brain as if it were the
left half. This is mentioned only to show that the model figured
is properly to be compared directly with H(^rrick's reconstruction.
The model shows the following points. TIk^ i)rim()rdium hippocampi is not so large as in I^ampetra but has the same form and
relations. The nucleus habenulae projects rostiad somewhat
over the primordium hippocampi. The sulcus limitans hi]^])ocampi and sulcus hypothalamicus very closely resemble those in
Lampetra. The emincntia thalami is better marked than in
Lampetra, being a ))r()iiiii)('nt ridge near the nucleus habenulae.
THE TELENCEPHALON IN CYCLOSTOMES 349
Behind the eminentia thalami is a ridge extending from the nucleus
habenulae to the interpeduncular region and occupied by the
tractus habenulo-peduncularis. Between this ridge and the eminentia thalami is a sulcus diencephalicus medius which is somewhat more regular than in Lampetra. The sulcus limitans of His
is somewhat less pronounced than in Lampetra.
Professor Herrick thought that he found in Ichthyomyzon conditions which supported his theory regarding the division of the
diencephalon and the telencephalon of amphibians into four longitudinal columns. In amphibians (Herrick, '10, p. 419) the sulcus
medius forms the dorsal boundary of the eminentia thalami and
runs caudally toward the tuberculum posterius. The statement
that this sulcus and the sulcus ventralis 'converge anteriorly to
the interventricular foramen' is evidently without foundation,
since the sulcus medius is situated dorso-caudal to the eminentia
thalami and the velum transversum, and can not reach the interventricular foramen. In the amphibians studied by the writer
(Amblystoma, Xecturus, Cryptobranchus, Rana, Bufo) the sulcus
medius runs up into the dorsal sac and has no relation to the interventricular foramen. This fact is clearly shown also in Herrick's
figures 5, 18, 19, 22, 33 and 34.
In Herrick's Ichthyomyzon figures 78, 79 and 80, the s.m. corresponds to my sulcus limitans hippocampi, while in figure 81
and on the right side of figure 80, s.m. is the sulcus hypothalamicus.
Consistent with his indentification of this with the sulcus medius,
Herrick labels the area below it as the pars ventralis thalami and
compares it with the eminentia thalami of amphibians ('10, p.
471). This interpretation is obviously untenable, since the
eminentia thalami of amphibians is caudo-dorsal to the interventricular foramen, immediately adjacent to the nucleus habenulae, is bounded below by the sulcus diencephalicus ventralis
and is traversed by the compact stria medullaris just before this
bundle enters the nucleus habenulae. See Herrick's figures 17to 22. The true position of the eminentia thalami in Ichthyomyzon is clear from Herrick's figures 80 and 81 in which the compact
stria medullaris is about to enter the nucleus habenulae. These
figures show that the eminentia thalami lies as in amphibians at
350 J. B. JOHNSTON
the dorsal border of the brain near the nucleus habenulae. This
is more clear from my figure 9 which is drawn from a section
l3etween the two drawn in Herrick's figures 80 and 81. In this
section the stria medullaris is seen in the eminentia thalami. In
Herrick's figure 81 the stria medullaris has bent laterad into the
outer portion of the nucleus habenulae and the tractus habenulopeduncularis is coming down near the ventricle. Having thus
identified the eminentia thalami, it is evident that the groove in
Ichthyomyzon which corresponds to the sulcus medius of amphibians is the groove so lettered in figure 6.
Professor Herrick has completely overloooked the greater part
of the sulcus limitans hippocampi in Ichthyomyzon, probably
because the greater part of its course lies more or less parallel
with the plane of the transverse sections. For the same reason
he failed to recognize that his s.m. and s.v. were the two ends of
one and the same crescentic groove. The model clearly shows
the true relations in both cases, and readily explains how natural
Professor Herrick's interpretation was in the absence of models.
In dealing with the relations of the telencephalon and diencephalon in the dorsal region. Professor Herrick ('10, pp. 473-4)
says,
On account of the very small degree of evagination of the cerebral hemisphere in cyclostomes the di-telencephalic fissure is shallow and the pars
dorsalis thalami passes over without interruption into the lat(^ral wall
(lobus olfactorius) of the hemisphere. Moreover this fissure do(^s not
extend upward to the mid-dorsal line and thus the dorso-median ridge
is able to pass continuously from one segment to the other. In higher
vertebrates this fissure extends dorsally up to the site of the vchmi transversum and it is so deep as to interrupt the continuity of both the ridge
and all other massive tissue of the pars dorsalis thalami with their telencephalic representatives.
It is necessary to define clearly what is meant by the di-telencephalic fissure. In the human and mammalian brain there
is a great groove or fissure between the posterior part of the
hemisphere and the thalamus, midbrain and cerebellum. Near
the bottom of this is the chorioidal fissure of the hemisphere.
Dorsally the fissures of the two sides join in the great longitudinal
fissure. Taken together these constitute in a true sense a nutrgi
THE TELENCEPHALON IN CYCLOSTOMES 351
ginal or limiting fissure of the hemispheres. It owes its existence
to the fact that the evagination of the hemisphere causes an angle
or fold between its wall and the wall of the brain stem. The
whole fissure may therefore be referred to under the descriptive
term, stem-hemisphere fissure. When lower vertebrates are
examined it is seen that the stem-hemisphere fissure is wellmarked in reptiles and amphibians, but in true fishes is only a
broad shallow groove or constriction. In Petromyzonts, one of
the most striking features is the sharp separation between hemisphere and brain stem (fig. 7). In a previous paper ('09) the
writer has shown that this is not the line of division between telencephalon and diencephalon. The groove seen in figure 7 running
from near the median line in front outward and backward is the
stem-hemisphere fissure. It marks the boundary between the
hemisphere and the telencephalon medium, not onlyincyclostomes
but in all classes of vertebrates. When the hemispheres expand
and lie apposed to each other in the median plane, this forms the
great longitudinal fissure and its lateral extension between the
posterior pole of the hemisphere and the brain stem.
Obviously this stem-hemisphere fissure can not be called a
di-telencephalic fissure. The writer has suggested ('09, p. 516)
that the di-telencephalic fissure owes its origin to the withdrawal
of tissue to form the optic vesicle. In this Professor Herrick
concurs ('10, p. 467). The di-telencephahc fissure lies at the
junction of the telencephalon medium and diencephalon, while the
hemisphere evagination takes place some distance farther rostrad,
and the two are entirely independent. That this is so is perfectly
clear from cyclostomes, selachians and other fishes. The evagination of the hemispheres has, therefore, nothing to do with the
di-telencephalic fissure or the continuity of diencephalon and
telencephalon. Further, the di-telencephalic fissure is dorsal in
position from the start and does not extend farther dorsally in
higher vertebrates. Wliat does happen is that in higher vertebrates more and more of the telencephalon medium comes to be
evaginated into the hemispheres until the stem-hemisphere fissure
gradually approaches the di-telencephalic fissure.
352 J. B. JOHNSTON
In cyclostomes the di-telencephalic fissure is as clearly present
as in other vertebrates. It is marked by the eminentia thalami
to which the velum transversum is attached. In the ammocoetes
of Petromyzon dorsatus, at least, the di-telencephalic boundary is
further marked by an external groove (fig. 4) . Professor Herrick
is in error in his speculations regarding the continuity of the dorsal
part of the thalamus and the telencephalon in cyclostomes (pp.
474 and 477-8) . The di-telencephalic fissure is slightly masked
in cyclostomes because of the crowding back of the telencephalon
against the diencephalon but the sulcus medius comes to the dorsal
border here precisely as in amphibians and if the dorsal column
is interrupted by the di-telencephalic fissure in amphibians, it is
interrupted in just the same way in cyclostomes.
Herrick states (p. 472) that he has indicated in figure 73 by a
dotted line (s.d.) 'a somewhat arbitrary boundary' between his
dorso-median ridge (my primordium hippocampi) and his pars
dorsalis thalami. This dotted line does not correspond to the
sulcus limitans hippocampi or to any thing that I can find in
Lampetra, Petromyzon dorsatus, Entosphenus or Ichthyomyzon.
The dotted line is lettered sulcus diencephalicus dorsalis while in
the text (p. 470) the dorsal is spoken of as synonymous with the
sub-habenular sulcus. In amphibians (Herrick '10, 431 and fig.
22) the subhabenular and dorsal sulci are distinct but are regarded
as two parts of a sulcus which separates the epithalamus from the
dorsal part of the thalamus. In amphibians the dorsal is the more
caudal segment of the common sulcus. In the Ichthyomyzon
diagram the positions are reversed. In amphibians neither of
these sulci has even a remote relation with the interventricular
foramen, and both lie wholly within the diencephalon. In the
Ichthyomyzon diagram the line s.d. is connected with the foramen
and lies wholly within the telencephalon. This arbitrary line in
Ichthyomyzon has therefore no relation to the sulcus diencephalicus dorsalis of amphibians.
Herrick regards the groove which extends rostrad from the
foramen as a continuation of the sulcus diencephalicus dorsalis.
In this position there are two grooves in Ichthyomyzon and in
Lampetra. One extends forward from the dorsal angle of the
THE TELENCEPHALON IN CYCLOSTOMES 353
foramen, the other from the ventral angle, and the two converge
into the nenroporic recess. The lower one of these grooves is the
one designated by Herrick as the telencephalic extension of the
sulcus dorsalis (Herrick '10, figs. 75, 76). The dorso-median ridge
(my promordium hippocampi) ends rostrally in the sections which
contain the so-called dorsal olfactory commissure. As seen in the
model, it is very abruptly reduced in dorso-ventral thickness at
the foramen and extends over the foramen only as a slender strand
of cells (which appears in Herrick's fig. 77) in close connection
with the commissure. Rostral to the foramen this slender ridge
disappears entirely and the larger ridge which Herrick calls the
dorso-median ridge in his figures 75 and 76 contains glomeruli and
olfactory fibers and belongs to the formatio bulbaris. Of the
two sulci extending rostrally from the foramen, the upper one
separates the dorso-median ridge (primordium hippocampi) from
the formatio bulbaris, the lower one separates the formatio bulbaris
from the medial olfactory nucleus.
In the ammocoetes of Petromyzon dorsatus (figs. 3, 8) there is
only one groove extending from the foramen to the neuroporic
recess. This sulcus separates the primordium hippocampi from
the medial olfactory nucleus and there is no formatio bulbaris
in this position . Lampetra presents an intermediate condition.
The two grooves are nearer together and the area of formatio
bulbaris which abuts on the ventricle is less than in Ichythyomyzon.
These facts show that in Ichthyomyzon and Lampetra the evagination of the hemisphere has not completely carried out the formatio
bulbaris, but that a part of this formation remains in the telencephalon medium and forms part of the wall of the median ventricle rostral to the foramen. In Petromyzon dorsatus the evagination of the formatio bulbaris is complete. Consequently, the
two sulci in Ichthyomyzon and Lampetra may be regarded as
merged into one sulcus in Petromyzon dorsatus. This one sulcus begins in the neuroporic recess and passes into the rostral
wall of the lateral ventricle, separating the primordium hip]30campi from the medial olfactory nucleus. The position of this
sulcus is the same as that of the medial zona limitans (hippocampi)
in selachians (Johnston, '11 a).
354 J. B. JOHNSTON
The brain of Professor Reighard's dwarf lamprey presents
larger hemispheres with wider lateral ventricles than I have seen
in any other petromyzont. In the form and size of the primordium hippocampi and in the disposition of the ventricular sulci
it agrees well with Lampetra.
The primordium hippocampi
The description of the ventricular sulci has made clear the
definite ventral boundary of this body on the ventricular side.
Externally a very deep groove separates it from the caudal pole
of the hemisphere (fig. 7), At the interventricular foramen the
primordium hippocampi bends through the roof of the foramen
to become directly continuous with the roof of the hemisphere.
Caudally, the sulcus limitans separates this body sharply from the
eminentia thalami and nucleus habenulae internally, but on the
external surface there is no visible boundary in adult Lampetra.
In the ammocoetes of Petromyzon dorsatus the external surface
shows a vertical groove which marks the caudal boundary of the
telencephalon (fig. 4).
The neurones of this body belong to a special type which is
found nowhere else in the brain of Lampetra. The same type of
neurone is characteristic of the primordium hippocampi of ganoids
and amphibians. As far as the writer's studies have gone, these
neurones are as truly characteristic of the primordium hippocampi
as are the Purkinje cells of the cerebellum, and are much more
highly differentiated in cyclostomes than are the Purkinje cells.
In a fomer paper ('02 a, p. 40) these neurones as they appear in
Golgi preparations were discribed as follows:
The cells of the cpistriatum are arranged in two to four rows adjoining
the cavity. The larger end of the p3'-ramidal cell body is next the cavity
and a large dendrite which arises from the apex divides into two or more
large branches which expand in the fiber layer. The dendrites bear
numerous small spines which are knob])ed at the end (fig. 26) in the
manner characteristic of the epistriatum, infV^rior lobes, and tectum of
Acipenser. These peculiar spines are found nowhere in the brain of
Petromyzon except on the epistriatum cells. These cells are so closely
similar to the epistriatum cells of Acipenser that it would be impossible
to mistake their identity.
THE TELENCEPHALON IN CYCLOSTOMES 355
The pyramidal body and the dendrites studded with knobbed
spines are so characteristic of these neurones that the resemblance
to the hippocampal cells in Acipenser, Amia and Rana is at once
striking and unequivocal. Examples of these cells in each of the
forms named are shown in figures 30 to 34, for comparison with the
cells in Lampetra. The bodies of the neurones in Lampetra stand
near the ventricle and their dendrites divide into a few relatively
straight branches which traverse the thickness of the wall, often
reaching the outer surface (figs. 30, 31).
When we look for the boundary between the primordium
hippocampi and the epithalamus, the internal structure as seen in
horizontal sections seems to furnish the necessary data. First,
there is no difference in the internal structure of the whole dorsomedian ridge bounded by the foramen and the sulcus limitans
hippocampi. Everywhere it is filled by the peculiar type of
neurones just described and nowhere is there any change of finer
structure which would lead us to say that any two or more parts
of it represent different functional centers. However, the moment
the sulcus limitans hippocampi is passed in any direction we come
upon neurones of types wholly different from those of this ridge.
This can not be accidental; it must be the expression of functional
differentiation.
The neurones of the so-called striatum have been described and
figured in my earlier paper ('02 a, figs 18, 19). They are bipolar
or multipolar cells with irregularly curved and branching dendrites
free from spines. The neruones of the nucleus habenulae have
also been figured ('02 a, fig. 16; this paper, figs. 17 to 20). They
are, like those in Acipenser, small cells with short very irregular
dendrites often with enlarged tips bearing tufts of small branches.
The subhabenular region is broadly continuous with the primordium hippocampi but the boundary line is very distinct in Golgi
sections. The type of neurones peculiar to the primordium hippocampi stops abruptly along a fine drawn latero-caudad from
the sulcus limitans hippocampi (see figures of horizontal sections,
18, 19, 20). At the same time along this same line end abruptly
the parallel fibers coursing lengthwise through this ridge. At
this line the fibers are cut off in horizontal sections because they are
356 J. B, JOHNSTON
turning up into the nucleus habenulae, as is seen in the most
dorsal sections. Compare figures 15, 16 and 19, 20. Behind the
line mentioned there is a wholly irregular tangle of nerve fibers and
farther back the fibers of the optic tract. Scattered among the
tangled fibers are bipolar and multipolar neurones with long sinuous dendrites devoid of spines. The type of structure of the two
bodies as a whole is as strikingly different as are the individual
neurones found in them.
In transverse sections, owing to the direct contiguity and the
oblique overlapping of the primordium hippocampi and the epithalamus, the boundary is of course not so clear, but there is a
very abrupt transition from one type of neurones to the other
which strongly suggests the distinctness of the two centers.
Tretjakoff ('09) gives a very imperfect description of the 'praethalamus' without figures. He states that its cells are much
like those of the thalamus and that the only afferent or efferent
tract connected with the praethalamus is constituted by the fibers
from the parapineal organ. These reach the praethalamus after
crossing, in the habenular commissure. The praethalamus serves
as a rudimentary perception center for the parapineal eye. ' ' Eine
andere Bedeutung des Priithalamus lasst sich bei Ammocoetes
kaum vermuten, da ungeachtet der grossen Zahl der Zellen der
Prathalamus von Ammocoetes, nach meinen Untersuchungen,
keine eigenen aus- oder zu fiihrenden Bahnen hat." The author
was evidently impressed with the inadequacy of the parapineal
tract to account for so large a center with a great number of cells.
This impresses us much more when we remember that the parapineal organ and tract exist only on the left side. According
to Tretjakoff's description the fibers cross in the commissure to
enter the fright) praethalamus. Hence the left 'praethalamus'
is wholly devoid of afferent fibers according to this author, and
we are led to suppose that a large center, rich in highly developed
cells exists in Ammocoetes totally without function. The writer
has found no evidence in his preparations that the parapineal
tract enters the 'praethalamus'.
Schilling C07) is inclined to the opinion that the 'praethalamus'
belongs to the telencephalon (p. 431 ; Herrick cites him erroneously
THE TELENCEPHALON IN CYCLOSTOMES 357
on p. 473) and points out that it is separated from the nucleus
habenulae by a deep ventricular sulcus. He did not distinguish
the characteristic cells of the ' praethalamus/ but describes the
passage through it of the bundles of the taenia thalami which
give off collaterals to it.
None of the authors who have studied the petromyzont brain
have used methods adequate to the differentiation of the types of
cells characteristic of the so-called praethalamus and the parts
adjacent to it. No method is so well adapted to this purpose as
the Golgi method and the description of this region given by the
writer in 1902 stands as the most complete heretofore given. That
description gave, however, a very incomplete account of the facts
shown in my preparations and the deficiency is to some extent made
up in the figures accompanying this paper. The 'praethalamus'
of authors is sharply distinguished from the epithalamus- and
thalamus not only by the ventricular sulci but by the well marked
characteristics of its cells and by the course of fibers which traverse
it.
Between this body and the roof of the hemisphere there is in
the same way a clear difference in the type of cells. This has
been sufficiently illustrated earlier ('02 a) and there is no dispute
among authors upon this point.
The fiber tracts related to the primordium hippocampi
These fiber tracts have been very imperfectly understood.
Both Schilling ('07, p. 432) and Tretjakoff ('09, p. 731) state that
no tracts connected with this nucleus were seen.
The stria medullaris is perhaps less complex in petromyzonts
than in the higher fishes, but at least four bundles related to the
telencephalon are present. (Fibers connecting the epithalamus
with other parts of the diencephalon will not be considered here) .
One of these bundles comes from the medial olfactory nucleus,
enters the primordium hippocampi near its rostral end above the
foramen and seems to pass over the dorsal ventricular surface of
this body to enter the nucleus habenulae (figs. 14 to 19, 25, 26,
35). It is by no means certain that this is a continuous tract.
THE JOURNAL OF COMPARATIVE >[EUnOLOGY, VOL. 22, NO. 4
358 J. B. JOHNSTON
A tract from the medial olfactory nucleus over the foramen interventriculare to the nucleus habenulae is not known in other vertebrates. The fibers passing up from the medial olfactory nucleus
as far as the primordium hippocampi occupy the same place as
the tractus olfacto-corticalis septi in selachians and amphibians.
If these fibers end in the primordium hippocampi, then what
appears to be the continuation of them to the nucleus habenulae
must be classed as cortico-habenular fibers. A second bundle
comes from the lateral and caudal walls of the hemisphere, passes
up behind the foramen through the inner and lower part of the
primordium hippocampi to join with the first as it enters the
nucleus habenulae (figs. 17, 18, 19). This is the tractus olfactohabenularis of authors. A third bundle comes from the preoptic
region and joins the first two (fig. 35). These three bundles unite
into a large compact bundle which traverses the eminentia thalami
at the bottom of the prehabenular recess and enters the nucleus
habenulae (figs. 19, 26, 27). The fourth component of the stria
medullaris is very diffuse and comes from the whole thickness of
the primordium hippocampi. Axones arising from the cells of
the primordium are seen in many cases passing at first peripherally
among the dendrites of these cells and then turning to run toward
the nucleus habenulae through the substance of the primordium
hippocampi. It is these fibers in addition to the first and second
bundles above described that give a longitudinal striation to the
whole of this body. At the caudal end of the primordium these
fibers enter the nucleus habenulae caudal and somewhat dorsal
to the compact bundle of the stria medullaris (figs. 16, 17).
The left nucleus habenulae is very small in Lampetra and nearly
all the left stria medullaris enters the superior commissure. In
the preparations from which figures 14 to 22 were drawn no fibers
were seen ending in the left nucleus. The view expressed in the
writer's paper on Acipenser ('01, p. 115) that the larger size of
the right nucleus is correlated with the ending of a larger portion of the tractus olfacto-habenularis in the right nucleus is
strongly supported in Lampetra. The superior commissure presents two main divisions, a more rostral, compact bundle and a
more caudal portion made up of sovcM-al strands (figs. 17, 18).
THE TELENCEPHALON IN CYCLOSTOMES 359
The rostral bundle is composed of fibers from the first bundle
described above and its fibers seem to end in the fiber-mesh of the
right nucleus (figs. 18, 19). The corresponding bundle of the
right side meets with the left and seems to end with it in the right
nucleus.
The strands of the more caudal division of the commissure are
made up of fibers of the remaining three bundles intermingled.
Many of these fibers end in the fiber mesh of the right nucleus
but many others pass through the nucleus without ending. This
is especially evident in such horizontal sections as those drawn in
figures 17 to 20. At least a part of these fibers clearly appear to
be those which arise in the primordium hippocampi. If so, it is
probable that these fibers end in the corresponding body on the
other side and are homologous with the posterior pallial commissure which is prominent in selachins, ganoids, teleosts and amphibians.
The fibers in the caudal division of the commissure which end
in the right nucleus may include those parts of the tractus olfactohabenularis which in other fishes arise in the lateral olfactory
nucleus and in the nucleus praeopticus. These may also include
fibers from the primordium hippocampi which would belong to
the tractus cortico-habenularis.
It seems reasonably certain from the study of these Golgi sections that the stria medullaris contains the equivalent of the
tractus olfacto-habenularis lateralis and posterior, and the commissura paUi posterior as described in the selachian brain. Nearly
all of these fibers from the left side cross in the superior commissure.
The writer has described ('02 a, pp. 38, 40) two afferent tracts
ending in the primordium hippocampi; one ascending from the
hypothalamus and one coming from the formatio bulbaris. The
former has since been called tractus pallii in all fishes and is regarded as the ascending gustatory tract entering the telencephalon
for the sake of correlation of gustatory with olfactory impulses.
This tract decussates in the post-optic commissure and ascends
over the internal face of the tractus opticus to enter the primordium hippocampi from below and behind.
360 J. B. JOHNSTON
The fibers which enter the rostral end of the primordium hippocampi from the formatio bulbaris are of coursepartof the olfactory
tract. In the previous description ('02a, p. 40) it was stated that
these come chiefly from the opposite side, crossing in the olfactory
decussation. The contribution of the commissure to the fiber
bundle entering the primordium hippocampi is illustrated in figure
24. Further study, both of the preparations used at that time
and of new preparations, has shown, however, that a much larger
number of direct fibers are present than was previously thought.
These fibers are soon mingled with the fibers of the first and second
bundles of the stria medullaris mentioned above and can not be
distinguished with certainty. It is clear, however, that many
fibers which enter from in front break up into end branches in
the primordium, hippocampi. Since we know of no other animals
in which olfactory tract fibers run without relay to the nucleus
habenulae, the presumption is strong that these olfactory tract
fibers end in the primordium hippocampi. This is the more probable in view of the fact that in selachians corresponding fibers are
present which end in the primordium hippocampi in part on the
same side and in part after crossing in a commissure situated above
the neuroporic recess.
Schilling and Tretjakoff both state that the fibers of the tractus
olfacto-habenularis give collaterals to the 'praethalamus.' Such
endings would represent a rudimentary tractus olfacto-corticalis.
On comparative grounds the presumption is strong that those
fibers mentioned above which run up form the medial olfactory
nucleus rostral to the interventricular foramen to enter the primordium hippocampi must constitute a tractus olfacto-corticalis.
The efferent tract from the primordium hippocampi has- thus
far been very imperfectly understood. The writer described fibers
descending to the 'striatum' and these have been confirmed by
Tretjakoff. These fibers are fine and do not appear in sufficient
numbers in my preparations to warrant the conclusion that they
represent the chief or only efferent path of this highly differentiated nucleus. Neither is it clear that they end in the ' striatum '.
It is possible that they pass through the 'striatum' but are not
iiiiprogDated beyond. Other fibers nuiy descend in the ti'a.ctus
pallii, as this tract in selachians and ganoids contains descending
THE TELENCEPHALON IN CYCLOSTOMES 361
fibers. The pathway by which the fornix columns run in all
higher classes is occupied by a broad bundle of fibers connecting
the medial olfactory nucleus with the primordium hippoc'ampi
(see above). If any fibers descend through this to reach the
hypothalamus, they would represent the fornix columns. We
must await further investigations upon these points.
We may now summarize the evidence for the interpretation of
this ' praethalamus ' or ' dorso-median ridge,' which has been
assumed in using the name primordium hippocampi.
(a) Its caudal end is just in front of the eminentia thalami to
which the velum transversum is attached. It is therefore wholly
within the telencephalon.
(b) It contains highly developed and specialized cells of a type
which is characteristic of the primordium hippocampi in selachians
ganoids, teleosts and amphibians.
(c) It is bounded by a ventricular sulcus which agrees closely
in position with the sulcus limitans hippocampi of selachians,
ganoids and teleosts.
(d) Along the lin^ of this sulcus there is a sudden change from
the characteristic cells to cells of very different form in the thalamus,
epithalamus and hemisphere. This abrupt change of structure is
comparable to the zona limitans of fishes and amphibians.
(e) It is traversed by a part of the tractus olfacto-habenularis
as in ganoids and teleosts.
(f) It has true commissural fibers passing through the superior
commissure as in fishes and amphibians (commissura pallii posterior) .
(g) It receives from in front fibers of the olfactory tract, direct
and crossed, comparable to those in selachians and in part to
those of ganoids and amphibians.
(h) It receives a tractus pallii ascending from the hypothalamus
as in all fishes. The center is therefore to be regarde'd as an olfactogustatory correlation center.
(i) It appears probable that there is a tertiary olfactory tract
ending in this body (tractus olfacto-corticalis).
Admitting such uncertainty as exists in the present state of our
knowledge regarding the posterior pallial commissure and the
tertiary olfactory connections, we have here a body of evidence
362 J. B. JOHNSTON
which leaves no reasonable ground for doubt that the body in
question is the homologue of the primordium hippocampi as
described in fishes and amphibians.
There is no ground whatever for Professor Herrick's assumption
('10, p. 473) that the greater part of this body belongs to the epithalamus, while a smaller rostral portion represents the primordium
hippocampi.
The fact of greatest interest regarding this body is, perhaps,
that the primordium of the visceral cortical complex of higher
animals (hippocampus, fornix, and related structures) remains in
cyclostomes in the telencephalon medium. As has been pointed
out in previous papers ('10 c, '11 a) the hemisphere evagination in
vertebrates involves at first only the primary olfactory centers and
it is only in later stages of phylogeny that the cortical substance
is evaginated.
Anterior pallial commissure
This has been known as the dorsal olfactory decussation, the
dorsal part of the anterior commissure, and by other names.
Schilling speaks of this as the anterior commissure and makes
only minor mention of the true anterior commissure. Schilling
recognizes in this dorsal commissure fibers connecting the formatio
bulbaris of the two sides and fibers connecting each formatio bulbaris with the opposite lobus olfactorius. The writer has described
fibers connecting the lobus of one side with the opposite primordium hippocampi. In addition, there are to be mentioned fibers
which come to the conunissure from the area of union of the caudal
wall of the hemisphere with the telencephalon medium (fig. 22).
A certain determination of the nature of these fibers depends
on the further study of the region from which they arise. They
may correspond to the fibei-s in selachians to which the writer has
given the namfi corpus callosum. The matter of greatest moment
in this connection is the existence in the lowest order of vertebrates of a commissure located in the lamina supraneuroporica.
The writer has shown elsewhere that the corresponding commissure
in selachians is large and important, and must reiterate the view
that this dorsal or supranoui'oporic commissure is primitive and
THE TELENCEPHALON IN CYCLOSTOMES 363
fundamental in vertebrates. A further examination of the palhal
commissures in reptiles and mammals with reference to this is in
progress (see '10 c).
Anterior commissure
This commissure is rather small in cyclostomes. It lies in the
lamina terminalis in front of the preoptic recess as in all vertebrates. Its constitution is not at all clearly known. Its fibers
probably come from the basal (lateral) olfactory area and the
so-called 'striatum.'
The 'striatum'
The region to which the name striatum has been applied includes
the supraoptic portion of the telencephalon medium and an
adjacent part of the hemisphere (figs. 5, 6, 22). It is clear that
this corresponds roughly to the striatum of other fishes. The
writer has shown ('02 a, p. 41) that the descending fibers from the
'striatum' go to the thalamus and not to the hypothalamus.
From this region fibers pass through the anterior pallial commissure, as noted above. These facts suggest that the striatal region
corresponds to or contains the equivalent of the somatic area of
selachians. Any decision on this point must await further study.
Mode of evagination of hemispheres. Zona limitans
The cyclostomes taken in comparison with higher forms give
clear evidence of the principle announced by the writer ('10 c,
'11a) that the hemispheres are lateral evaginations of the telencephalon which have gradually involved the formatio bulbaris,
the lobus olfactorius and the pallium in the order named. The
comparison of the cyclostomes with selachians and amphibians
with reference to the mode by which the more fully evaginated
brains have come to have their present form, is very important
for the interpretation of these higher brains.
If attention be given to the models shown in figures 5, 6 and 7,
it will be seen that the further evagination of the hemisphere
involves the turning out of the primordium hippocampi and the
364 J. B. JOHNSTON
striatal area through the foramen into the caudal portion of the
hemisphere. Somewhat more than the rostral half of the hemisphere is occupied by formatio bulbaris. The further evagination
would enlarge the caudal part of the hemisphere until it became
larger than the rostral part. At the same time the hemisphere
is drawn forward by- the elongation of the rostrum, the olfactory
bulb becomes separated form the caudal part of the hemisphere
and a longer or shorter tractus olfactorius or olfactory peduncle is
established.
The relations of the primordium hippocampi to the roof of the
enlarging hemisphere are especially interesting. We have pointed
out that there is an abrupt change of structure between the primordium and the roof of the hemisphere which may be called a zona
limitans. As the primordium hippocampi pushes out into the
roof of the hemisphere this zona limitans would be placed successively farther and farther laterad in this roof. In selachians
('11 a) this zona limitans runs from the olfactory peduncle backward along the dorso-lateral wall of the lateral ventricle. For
a long time in the phylogeny there remains a portion of the primordium hippocampi in the telencephalon medium extending along
the dorsal border of this region to the point of attachement of the
velum trans versum to the eminentia thalami. In this position,
where the whole of the primordium is located in cyclostomes,
there exists in Chimaera ('10 d) and selachians ('11 a) a slender
ridge of gray matter accompanied by the fibers of the posterior
pallial commissure. In ganoids and teleosts ('11 b), where the
evagination of the hemispheres has been arrested, the primordium
has retained in the caudal part of the telencephalon essentially
the relation which it holds in cyclostomes and has taken part in
the eversion of the forebrain. In amphibians the evagination has
gone farther than in selachians, the primordium hippocampi occupying the roof portion of the hemisphere and the zona limitans
being carried farther down in the lateral wall. There is still left
in the telencephalon medium, however, a small part of the primordiuH) hippocampi corresponding to that in selachians, although
shorter (Johnston, '00). Herrick ('10, p. 476) has endeavored to
show that this structure belongs to the eminentia thalami. It
THE TELENCEPHALON IN CYCLOSTOMES 365
is of course directly adjacent to the eminentia thalami and Professsor Herrick has apparently thought that more was to be included
in the unevaginated primordium hippocampi than the writer
intended. This structure is the continuation of the fimbriaborder of the hemisphere into the dorsal border of the telencephalon
medium until it meets the eminentia thalami. This small remnant of the primordium is seen in a model of the forebrain of
Necturus standing vertically rostral to the eminentia thalami and
separated from the latter by a groove. Figure 36 will show more
clearly the relations of this structure. Deep fibers related to the
cells of this unevaginated body enter the hippocampal commissure
as already described.
As the evagination proceeds the caudal part of the hemisphere
soon extends rostrad beyond the level of the interventricular
foramen and the lamina terminalis. This is already true in selachians and in amphibians and reptiles the hemisphere protrudes far
rostrally (fig. 37). In selachians, it has already been pointed out
that the sulcus limitans hippocampi continues rostrally beyond
the laterally placed olfactor}^ peduncle and encircles the rostral
wall of the hemisphere to end at the neuroporic recess (figs. 38,
39). This portion of the sulcus was called the medial sulcus
limitans hippocampi. As compared with cyclostomes, the condition in selachians has resulted from the continued evagination
which has carried the olfactory bulbs far laterad and has brought
the greater part of the primordium hippocampi into the roof of
the hemisphere. The region of the medial olfactory nucleus has
bulged forward beyond the lamina terminalis, and the sulcus which
separates the primordium from the medial olfactory nucleus in
front of the interventricular foramen in Petromyzon comes inselachians to lie in the medio-rostral wall of the hemisphere. In
both classes it runs from the neuroporic recess into the lateral
ventricle and marks the line of separation of the same structures.
It is properly called the sulcus (or zona) limitans medialis. In
amphibians the conditions are essentially the same (fig. 37).
Professor Herrick's view as to the evagination of the hemispheres
and the relation of his four columns to them is summarized in
the following paragraph ('10, p. 477) :
366 J. B. JOHNSTON
The roof plate and floor plate converge into the lamina terminalis,
where of course they end. The four massive columns on each side converge into the interventricular foramen, and in latvae with wide foramina and adult urodeles they may be followed through the foramina
into the evaginated hemispheres. Bearing in mind the fact that during
development the roof plate and floor plate retain permanently their
primitive attachments to the lamina terminalis, and that it is only the
massive lateral columns which are evaginated into the hemispheres, it
clearly follows that these columns of the diencephalon are continued into
the hemispheres in the form shown by the accompanying diagram (fig.
84), the zona limitans lateralis representing the locus of the sulcus medius
and the zona limiants medialis the line of union of the dorsal and ventral
columns in the lateral evaginations rostral to the fusion of the roof plate
and floor plate in the lamina terminalis.
It has been noted elsewhere ('lib, p. 540) that the assignment of
the lamina terminalis in this paragraph to the floor plate was an
error of inadvertance. It has been shown also ('11 b, pp. 534,
535 and in this paper) that the sulcus diencephalicus medius has
no relation with the interventricular foramen or the zona limitans
lateralis either in amphibians, fishes or cyclostomes.
The conception of the folding over of the lateral walls of the
diencephalon illustrated in Professor Herrick's figures 83 and 84,
such that the dorsal and ventral borders fuse in the medial zonae
limitantes to form two tubes extending forward (the hemispheres),
seems to the writer to be without basis in fact.
In figure 72 Herrick ('10) has given a diagram of the forebrain
in a hypothetical vertebrate ancestor. In this the representation
of the sulcus dorsalis is subject to the criticisms made above (p. 352).
No ground is given for the assumption that the retinal area does
not involve the dorsal border of the brain, except the erroneous
supposition that there is no di-telencephalic fissure in cyclostomes.
The sulcus medius is represented as a horizontal sulcus extending caudad from the site of the interventricular foramen,
whereas in all lower vertebrates it runs nearly vertically up into
the dorsal sac. The sulcus ventralis should lead to the site of
the interventricular foramen as it does in cyclostomes, selachians
and amphibians. The terminal ridge is represented as an independent thickening rostral to the chiasma ridge, whereas the terminal ridge in all vertebrate embryos itself becomes the bed for
the optic chiasma (Johnston '09).
THE TELENCEPHALON IN CYCLOSTOMES 367
SUMMARY
The evagination of the hemispheres is at a low stage in petromyzonts. In Ichthyomyzon and Lampetra the formatio bulbaris
is not all evaginated. The fact that a part of the wall of the third
(median) ventricle in these forms is made up of formatio bulbaris
ought to be convincing evidence, if any further evidence is needed,
that a part of the third ventricle belongs to the telencephalon. A
large part of the secondary olfactory centers is evaginated, but
a relatively much larger portion of these centers remains in the
telencephalon medium than in the case of selachians. The primordium hippocampi remains wholly in the telencephalon medium.
The exact relations of the somatic area await further study.
The di-telencephalic boundary is marked by the attachement
of the velum transversum to the eminentia thalami as in selachians
ganoids and amphibians. The eminentia thalami is a well-marked
ridge just rostral to the nucleus habenulae, bounded by the sulcus
medius and by the sulcus limitans hippocampi, and traversed by
the stria medullaris.
The telencephalon medium, which is relatively larger than in
higher vertebrates, stands as a wedge-shaped mass between the
hemispheres. Its massive nervous walls are connected with one
another by the lamina terminalis, lamina supraneuroporica and
tela chorioidea. The membranous roof plate (His) in the telencephalon of petromyzonts connects the two simple unevaginated
lateral walls of the neural tube as in any other segment. The
hemispheres are evaginations of restricted areas of these lateral
walls. The foramen is roofed over by the massive primordium
hippocampi and there is no extension of the tela chorioidea into
the roof of the hemispheres.
The primordium hippocampi is represented by the 'praethalamus' of previouls authors (the epistriatum of my earlier paper, '02
a). It is a large body having a highly developed and characteristic
finer structure which already presents most of the relations of the
primordium hippocampi of higher forms (see text). The two
primordia converge forward to form a bed for the anterior pallial
commissure in the lamina supraneuroporica. The primordium
is separated from the epithalamus, thalamus, hemisphere and the
368 J. B. JOHNSTON
medial olfactory nucleus by a sulcus liniitaiis hippocampi. Along
the line of tJiis sulcus is a sudden change of structure which may
be compared with the zona limitans of fishes and amphibians.
In vertebrates above cyclostomes the primordium hippocampi
is gradually evaginated into the hemisphere, the process being
complete in the reptiles. It is only as the hippocampus is carried
into the medial border of the hemisphere that the tela chorioidea
comes to foi'm the roof of the interventricular foramen and to
extend into the roof of the hemis])liere.
The expansion of the hemisphere carries both the primordium
hijipocampi and the medial olfactory nucleus rostrad beyond the
lamina terminalis where they form the medial hemisphere wall.
The sulcus limitans hipi)()campi which separates these two nuclei
in the telencephalon medium in petromyzonts becomes the sulcus
limitans mc^lialis hip})oca!ui)i in the hemisphere of selachians,
amphibians and reptiles.
The relation of the primordium hippocami)i to the lamina supraneuroporica in which the anterior pallial commissure lies is fundamental in vertebrates and nuist be taken into account in seeking
the interi)retati()n of higher brains.
The read(^i- is refei-red to the extended discussion of forebrain
morphology contained in the writer's paj)er on selachians ('11 a,
p. 37, esi)ecially pp. 47-52). The features of the evolution of the
forebrain upon which the cyclostome brain throws light especially
are briefly the following.
(a) The hypertrophy, rising dorsad and eversion of the olfactogustatory correlation center, "^riie same thing occurs in the visceral receptive column in the medulla oblongata of many fishes
and the nucleus habenulae conunonly.
(b) The presence originally of the whole olfactory central apparatus in the wall of the medial ventricle. Hemispheres are formed
bv the evagination first of formatio bulbaris, then secondary
olfac^tory centers, and last the visceral and somatic correlating
c(Milers which furnish the matcM-ials for the development of the
cortical structures.
(c) From a condition like that of cyclostomes the sehichian
telencephalon has been derived by the evagination chiefly of the
THE TELENCEPHALON IN CYCL0BT()ME8 'M)\)
medial olfactory nucleus and the primordium hippocampi. In
(C'himaera), ganoids and teleosts the evagination has been arrested
and the eversion of the primordium hippocami)i seen in cyclostomes
is greatly increased. The formatio bulbaris actually bounds the
median ventricle near the foramen and the apparent folding out of
of the striatal or somatic area in cyclostomes is absent in ganoids
and teleosts (see '11 b).
(d) The primitive relations of the hippocampal primordium
and of its commissure in the lamina supraneuroporica are splendidly
clear and instructive in cyclostomes. The selachians present
essentially the same relations in evaginated l)rains. In ganoids
and teleosts ('11' b) the extreme eversion has abolished the primitive supraneuroporic commissure, except in a few forms. In the
amphibians the commissures are similar to those of ganoids. In
reptiles and mammals the cyclostome and selachian condition
reappears.
(ej The view of the general mori)hology of the telencephalon
previously expressed ('10 c, '11 a, '11 b) receives the strongest
support from these most primitive brains. The functional columns
of the brain described by the writer ( '02 b) extend forward to the
telencephalon. The ventral columns are represented only by correlating tissue adjacent to the terminal ridge or optic chiasma.
The dorsal columns constitute the overwhelming part of the telencephalon, are greatly hypertrophied and become flexed in consequence. The dorsal and ventral columns meet in the preoptic
recess where the sulcus limitans of His ends. The telencephalon
in petromyzonts is not elongated parallel with the long axis of the
fish, but owing to its flexure, is longer dorso-ventrally.
The olfactory nerve and sac on the one hand and the formatio
bulbaris on the other are closely related to the neuroporic recess
and illustrate clearly the principle ('11 a, p. 39) that the neuroporic
recess owes its existence to the attachment of the olfactory nerve
to the dorsal lip of the neural tube at this point. The evagination of hemispheres began here close to the dorsal border at
some distance from the anterior end of the brain tube. This
point lies at about the middle or height of the forebrain flexure.
370 J. B. JOHNSTON
Caudal to this middle point of the forobraiii the visceral recepti\'c column forms the olfacto-gustatory correlation center or
primordium hippocampi. From the study of other fishes ('11 a
and '11 b) I have shown reason to think that the somatic correlation center, or primordium of the somatic cortex has been formed
by eversion and mij>;rjiti()n of neuroblasts from the dorsal border of
the telencephalon in this caudal part.
The ce})halic part of the forebrain comes to be ventrally ]ilaced
owing to the flexure, and is constituted chiefly or wholly of the
medial and lateral secondary olfactory centers and preoptic
nucleus. The foi-matio bulbaris arises from tissue nearest the
olfactoi-y nerve root at the middle i)ai't of the dorsal colunm and
in higher forms is carried out upon a peduncle. In some petromyzonts it actually retains its relation to the median ventricle.
An undei'standing of the fundamental morphological and functional relations in the forebrain must be built upon the central
fact of the forebrain flexure. The conception of a curved axis of
the telencephalon ending at the i)reoptic recess, and of the olfactory nerve entei'ing the doi-sal boi'der at the height of the curve
must never be lost sight of. These are fundamental facts, not
hypotheses, and all forebrain morphology becomes confused unless
these facts are held firmly in mind.
In forms above the cyclostomes the rostrum elongates, the olfactory sac shifts forward, the bulbar formation follows it and becomes
pedunculated. At the same time the evagination of hemispheres
progresses rapidly and the hemispheres elongate. Now the cephalic and caudal portions of the visceral receptive colunm are
sharply flexed on one another in the form of a letter U (figs. 40,
41). The olfactory tract enters the curve of the U. The cephalic
limb, containing the secondary olfactory centers is ventrally placed
and ends at the ])reo})tic recess. The caudal limb (pi'imordium
liippocampi) is dorsally placed and ends at the eminentia thalami.
The two limbs are sej)arated by the interventricular foramen and
by the medial and lateral zona limitans as already explained.
Owing lo the eversion and migration of the neuroblasts of the
somatic correlatiiig centci- down u|)()n llu> lateral surface of the
telencei)h;tlon Ihis priinoidiuni of (lie geiiei-al coi'tex comes to lie
THE TELENCEPHALON IN CYCLOSTOMES 371
between the limbs of the U. In this position it enters into relations with the lateral olfactory nucleus which lead to the formation
of the pyriform lol)e as an olfacto-somatic correlation center
(cortex) . Within the somatic primordium there develop also complex correlation systems between the cutaneous, musculo-sensory,
auditory and visual fi})er tracts which probably reach this center at
an early stage in the phylogeny (see '10 c, and '11 a). This complex correlating organ is the general cortex. As it develops it
pushes in between the primordium hippocampi and the pyriform
lobe, assuming the characteristic postion of the general cortex
in mammals. The expansion of the general cortex pushes the
hippocampal formation to the medio-dorsal border of the hemisphere and the pyriform lobe down to the ventral surface.
litj^:ratiire c^ited
BuRCKiiAKDT, RuDOLF 1894 b Die Homologien des Zwischenhirndiichcs bei Kcp
tilien und Vogoln. Anat. Anz., Bd. 9.
1894 (• Zur vergleichenden Anatomie des Vorderhirns l)ei Fischcn.
Anat. Anz., Bd. 9.
1907 Das Zentral-Nerven.system der Selachior. I. Teil: Einlcitung
und Scymnus liohia. Abhdl. der Kais. Leop. -Carol. Doutsch. Akad.
Naturf., Bd. 73. Halle.
Herrick, C. Judson 1910 b The morphology of the forcbrain in Amphibia and
Reptilia. Jovir. Comp. Neur., vol. 20.
Johnston, J. B. 1901 The brain of Acipenser. Zool. Jahrb., Anat., Bd. 15.
1902 a The brain of Petromyzon. Jour. Comp. Neur., vol. 12.
1902 b An attempt to define the primitive functional divisions of the
central nervous system. Jour. Comp. Neur., vol. 12.
1906 Nervous system of vertebrates. Philadelphia, Blakiston.
1909 b The morphology of the forebrain vesicle in vertebrates. Jour.
Comp. Neur., vol. 19.
1910 c The evolution of the cerebral cortex. Anat. Ilcc, vol. 4.
1910 d A note on the forebrain of Chimaera. Anat. Anz., vol. 30.
1911 a The telencephalon of selachians. Jour. Comp. Neur., vol. 21.
1911 b Telencephalon of ganoids and teleosts. Jour. Comp. Neur.,
vol. 21.
K.vppERS, C. U. ARiiiNS and Carpenter, F. W. 1911 Das Cehirn von Chimaera
monstrosa, Folia Neuro-Biologica, Bd. 5.
Schilling, K. 1907 Ueber das Gehirn von Petromyzon fiuviatilis, Abhdlg. d.
Senekenb. Naturf. Ges., lid. .30.
Sterzi, G. 1907 II sistema nervoHo centrale dei vertebrati. Vol. 1, Ciclostomi.
Tretjakoff, D. 1909 Das nervensystem von Ammocoetes. II Gehirn. Archiv
Mik. Anat., P.d. 74.
372
J. B. JOHNSTON
REFERENCE LETTERS
b.o., bulbils olfactorius, formatio bulbaris.
c. a., commissura anterior
ch., chiasma opticum.
c.Mpp., commissura hippocampi.
c.p., comiriissura posterior.
c.-p.a., commissura pallii anterior.
c.p.p., commissura pallii posterior.
c.sup., commissura superior (Osborn).
dienc, diencephalon.
di-tel., di-telencephalic boundary.
d.p., decussatio postoptica.
e., epiphysis.
em.th., eminentia thalami.
/.{., foramen interventriculare.
f.olf., fila olfactoria.
f.p.p., fibers from the parapineal body.
g., olfactory glomeruli.
hem., hemisphere.
hy., hypophysis.
hyp., hypothalamus.
I.O., lobus olfactorius (secondary centers).
I.S., lamina supraneuroporica.
l.t., lamina terminalis.
I. v., lateral ventricle.
in., caudal margin of lamina supraneuroporica.
mesenc, mesencephalon.
n.h., nucleus habenulae.
n.olf., nervus olfactorius.
V. Ir., velum
nuc.olf.7ned., nucleus olfactorius medi
alis.
par., paraphysis.
p.c.b., precommissural body.
p.h., primordium hippocampi.
p.p., parapineal body.
pt., pretectal region.
rec.ph., recessus praehabenularis.
r.m., recessus mammillaris.
r. n., recessus neuroporicus.
r.p., recessus praeopticus.
r.po., recessus postopticus.
s.d., saccus dorsalis.
S.I., sulcus limitans hippocampi.
S.I.H., sulcus limitans of His.
s.tii., stria meduUaris.
s. m. 1, first bundle of stria medullaris
s.med., sulcus diencephalicus medius of
Herrick.
s.hy., sulcus hypothalamicus.
sub.hab., subhabenular region.
t.c, tela chorioidea.
tel.m., telencephalon medium.
t.f., taenia fornicis.
thai., thalamus.
t.p., tuberculum posterius.
tr.c-h., tractus cortico-habenularis.
ir.h-p., tractus habenulo-peduncularis.
Ir.o-h., tractus olfacto-habenularis.
tr.op., tractus opticus.
tr. pall., tractus pallii.
transversum.
Fig. 1 The medial surface of the right half of the brain of Mustelus to show
the position of the velum transversum in selachians. It is attached to a slight
eminentia thalami which is not lettered.
Fig. 2 Medial view of the right half of the telencephalon and diencephalon of
an adult Acipenser. The olfactory Ijull) is not drawn. The velum transversum is
a very deep fold of the tela chorioidea which is nearly horizontal in position. It
is attached to the eminentia thalami as in selachinas, amphibians and others.
THE TELENCEPHALON IN CYCLOSTOMES
.373
Paraphysis
Telencephalon
Nucleus habenuiae Tectum mesencephali
Velum transversum y' ,-—
Epiphysis / V" ~—
■ i
Cerebellum
Lob. lin. lat.
Tub acust.
Rec. neurop.
Rec. praeop.
Sac. vase.
Com. infima
Lobus visceralis
Lobus inferior
Optic chiasma
THE JOURNAf, OF COMPARATIVK XK rHOI.Oc ; Y, VOL. 22, NO. 4
374 J. B. JOHNSTON
Fig. 3 Petromyzon dor.satus, ammocoetes. Medial view of a model of the
left half of the forebrain.
Fig. 4 Lateral view of the model shown in figures. The hemisphere is divided
by a vertical sulcus into a rostral portion containing the bulbar formation and a
caudal portion containing the secondary olfactory centers. About opposite the
caudal pole of the hemisphere appears a vertical sulcus in the wall of the brain
stem. This corresponds in position to the di-telencei)halic boundary line as determined by other data and is to be regarded as a di-telencephalic sulcus or fissure.
THE TELENCEPHALON IN CYCLOSTOMES
875
p.a.
J. B. JOHNSTON
Fig. o Lanipotrji vvildcri. Medial view of I lie ri>ilil lialf of a model of llio
tcU'iicephulon and dienccphah.ii. X •">().
THE TELENCEPHALON IN CYCLUSTOMES
377
Fig. 6 Ichthyomyzon concolor. Medial view of the right half of a model of
tne telencephalon and diencephalon. X 66. The slender groove rostral to the
sulcus medius is apparently due to one or two sections being less stretched in mounting than the adjacent ones.
378
J. B. JOHNSTON
Fig. 7 Lunipct ra. Dorsal view of llie model shown iu figure 5. This is presented chiefly to illustrate the stem-heniisphere fissure and the wedge-shaped
telencephalon medium. The attached Iiordcr of the tela chorioidea is drawn.
Its caudo-lateral angle is the upper end of I he iccessus praehabenularis. In
Petromyzon dorsatus the eniinentia thalumi comes up nearly to this point and the
velum traiisversum is attached to it. The broken line running caudo-laterad
from this point corresjxdids lo llic plane of sudden transition in internal sliiicturc
from the primordium hipiJocain])i lo the pretectal and subhabenular region.
THE TELENCEPHALON IN CYCLOSTOMES
379
i.sand CI
Vent. Ill
Fig. 8 Petromyzoii dorsatus, ammocoetes. Model of the dorsal portion of the
left half of the forebrain, drawn as seen from the medio-ventro-caudal direction.
The model was carefully constructed on a large scale in order to determine whether
the velum transversum really formed a continuous fold from the median line to
the lateral attachment of the tela (i. e., the taenia). This drawing should be compared with figures 23 to 27. d.m.c, dorsal sac.
380 J. B. JOHNSTON
Fig. 9 Ichthyomyzon coiicolor. A tran.svcrse section tlirough the mu'leus
habenulae and eminentia tlialami of tlie right side. The section cuts the cminentia thalami at its most prominent part, where it is bounded by the sulcus limitans
hippocampi below and the sulcus subhabenularis above, as seen in figure (i.
Fig. 10 Petromyzon dorsatus, adult. Transverse section through the interventricular fommen. The primordium hippocampi is not so large as in Lani])etra.
At the lip of the foramen it is continuous with the wall of the hemisphere.
Fig. 11 Same series as figure 10, section through the eminentia thalami.
Fig. 12 Entosphenus, ammoccetes of 35 mm. Transverse section through
rostral part of foramen interventriculare. The section is quite oblique so that
on the right side it passes considerably rostral to the foramen. The primordium
hippocampi is small but occupies the same position as in other forms. The section
falls at the junction of the parapineal body and the left nucleus habenulae.
Fig. 13 Same series as figure 12, section through the eminentia thalami and
the habenular nuclei. Note the great size of the right nucleus habenulae. On
the right side the primordium hippocampi is cut.
THE TELENCEPHALON IN CYCLOSTOMES
381
382 J. B. JOHNSTON
Figs. 14-22 Lampetra. Nine sections of the habenular and hippocampul
region drawn from a series of horizontal sections prepared by the Golgi method.
The figures were drawn at a magnification of 200 diameters and are reduced to onethird. Figure 22 is at a somewhat lower magnification.
Fig. 14 The first section through the dorsal part of the left primortlium hij)i)ocampi. The section shows the epiphysis and its stalk. The four fibers in the left
nucleus habenulae come from the parapineal body. The bundle s.m.l is the first
part of the stria medullaris of which it is uncertain whether it is a tractus olfactohabenularis or tractus cortico-habenularis.
Fig. 15 The second section of the same series. The first bundle of the stria
medullaris is passing through the left nucleus habenulae.
THE TELENCEPHALON IN CYCLOSTOMES
383
384
J. B. JOHNSTON
^trc-h
i'iji. K) 'I'lic lliird section of tlic same sprios. Note the (>\trciTic difTcrcnco
in size botwocn the two nuclei lial)cniilae and tlic passage of the first stria luedullaris fibers as a compact bundle over to the right nucletis. The i)rehabenular
recess is narrow in L.iuipel ra and t lie etnincntia thalanii does not appear as a distinct rifltie in t \icsc dorsal sect ions. This is due to the \avg,v size of t lie i)rirnoi<liuni
hippociiiipi in l-anipetia as well as to the crowding together on account of the
[)ressure of the buc<-al fuiuiel. A section through the brain of Iclit liyoniyzon or
I'r'trornyzon dorsatus at this same level would show a distinct emincnlia thalanii.
( 'ornpare figures (> and '■).
THE TELENCEPHALON IN CYCLOSTOMES
385
Fig. 17 The fourth section of the same series. Xote the several divisions of
the commissura superior (Osborn). The next three figures show that the great
majority of the left stria medullaris decussates and that a large number of fibers
pass through the nuclei habenulae to the opposite primordium hippocampi.
386
J, B. JOHNSTON
Fig. l.S The iil'Ui section of t he same series. The right i)riinor(liuiii hippocampi
shows the first stria medullaris bundle. On the left the tractus olfacto-hahenularis comes up through the lower part of the primordiuin hippocampi and the
ciniiicnt ia thalami.
THE TELENCEPHALON IN CYCLOSTOMES
387
Fig. 19 The sixth section of the same series. On both sides the fibers of the
tractus olfacto-habenuhiris lateralis and posterior appear as definite bundles which
in the next sections clearly lie in the eminentia thalami.
388
J. B. JOHNSTON
Fit--. ■_'ll 'l"li<' scvciitli soclioii of the s:inio >^oi-ics. In tlu' r^.slral pml cf the
rijrht |.rin,(,nliu.n liipiuu'iunpi is s.'.'ii a cell wlms.' ax(,nr is .linTt..! tuwanl Uic
n.idcus hiUH'imhic. Xotc the shiirpncss of li.c slnnMural l...inwlaiy iHfwcri, 1 he
primonlium hippociiinpi and the piclcctai region.
THE TELENCEPHALON IN CYCLOSTOMES
389
Fig. 21 The ninth section of the same series. Note the difference between
the cells in the primordium hippocampi and those in the subhabenular region.
The tractus olfacto-habenularis occupies a position in the eminentia thalami
which is quite typical for vertebrates generally. The great number of longitudinal fibers in the primordium hippocampi are only indicated by a few lines.
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 4
390
J. B. JOHNSTON
Fig. 22 The thirteenth section of the same series drawn at a lower magnification. The section passes through the anterior pallial commissure and above the
interventricular foramen. The heavy broken line shows the outline of the next
section ventrad, in which the sulcus limitans hippocampi passes forward to enter
the foramen. Note that the primordium hippocampi is followed caudally by the
eminentia thalami and this by the ridgo containing the tractus habonulo-peduncularis. The sulcus medius separates these two ridges. The anterior pallial commissure in this section has only fibers connecting the hemispheres.
THE TELENCEPHALON IN CYCLOSTOMES
391
392 J. B. JOHNSTON
Figs. 23-27 Ammoecoetes of Petromyzon dorsatus. Five sections from the
sagittal series from which the model shown in fig. 8 was reconstructed. The
outlines were made with the aid of the Edinger drawing apparatus. The velum
transversum is seen as a distinct fold of the tela in figures 23 to 26, but in figure
27 it joins the eminentia thalami. Figures 25 and 26 show well the course of the
tract which runs up from the medial olfactory nucleus in front of the foramen
interventriculare. This bundle may contain a tractus olfacto-corticalis and possibly also the fornix column. The fibers of the commissural bundles beginning
with the most rostral successively turn up into the primordium hippocampi (fig.
24). The fibers which go laterally into the hemispheres are not readily seen in
these sagittal sections because they are cut across. These sections show conclusively that the commissure is largely related to the primordium hippocampi.
THE TELENCEPHALON IN CYCLOSTOMES
393
394
J. B. JOHNSTON
Fig. 28 A diagram to show the disposition of the velum transversum. The
outline is taken from figure 7, showing the dorsal aspect of the model of the Lampetra brain. The tela chorioidea is drawn as it would appear if the epiphysis and
parapineal body were removed. The velum transversum is drawn as a fold of the
tela.
Fig. 29 Professor Herrick's figure 73 reprinted for comparison with figures G
and 9 of this paper. The figure is "a diagram reconstructed from actual sections
of the cyclostome brain, Ichthyomyzon concolor."
THE TELENCEPHALON IN CYCLOSTOMES
395
Fig. 30 Lampetra. Transverse section through the caudal third of the left
primordium hippocampi. Golgi method. Most of the dendrites are longer than
they appear in this figure. The distal ends of the dendrites extend nearly to the
outer surface but are too intricately interlaced to be followed.
396
J. B. JOHNSTON
Fig. 31 Lampetra. Transverse section through the priniordiuni hippocampi
just caudal to the interventricular foramen and the anterior j)allial commissure.
The cells in the rostral end of the primordium are of the same type as in the caudal
part (fig. 30).
THE TELENCEPHALON IN CYCLOSTOMES
397
Fig. 32 Acipenser rubicundus. Five cells of the i)iimordiurQ hippocampi for
comparsion with those of Lampetra. Note that the eversion of the forebrain in
this ganoid of 30 cm. is about the same as in the adult Lampetra.
398
J. B. JOHNSTON
Fig. 33 Amia calva, about 15 mm. A parasagittal section near the lateral
border of the forebrain, showing three cells of the primordium hippocampi and a
few fibers of the tractuspallii. (Jolgi method.
THE TELENCEPHALON IN CYCLOSTOMES 399
Fig. 34 Rana. Transverse section of the dorso-medial angle of the right
hemisphere showing the characteristic cells of the primordium hippocampi. Golgi
method.
400
J. B. JOHNSTON
Fig. 35 Scheme of fiber tracts related to the primordium hippocampi in petromyzonts. The secondary olfactory neurones located in the caudal part of the
hemisphere are represented by broken lines.
THE TELENCEPHALON IN CYCLOSTOMES
401
Fig. 36 Cryptobranchus allegheniensis. Transverse section through the telencephalon behind the cerebral commissures. The remnant of the primordium
hippocampi in the telencephalon medium appears on the left side to the right of
the letters p.h.
Fig. 37 Necturus. Sketch of the right half of the forebrain as seen from the
medial surface. This figure is introduced merely to show the general relations of
the medial zona limitans which extends rostrally from the interventricular foramen
and separates the medial olfactory nucleus and primordium hippocampi. Its
formation has been brought about by the evagination of the region which in the
brain of cyclostomes lies rostral to the foramen. Compare figure 5.
402
J. B. JOHNSTON
s.n.
olf.ped.
n.term
39
Figs. 38 and 39 Two drawings of a clay model made to represent a simplified
selachian forebrain. From Johnston '11 a. Figure 38 shows the medial surface,
figure 39 the rostral surface. The broken line on these surfaces represents the
medial zona limitans hippocampi. It extends from the neuroporic recess through
the interventricular foramen along the medial wall of the hemisphere. Compare
the figures of sections in the paper referred to. This zona limitans is homologous
with the line of separation of the prirnordium hippocampi and medial olfactory
nucleus rostral to the foramen in cyclostomcs. See figures 3, 5 and 6. In figure
.38, s.M. marks the continuity of the sulcus limitans hipi)ocampi with the sulcus
hypothalamicus, very much as in Lampetra and Ichthyomyzon. Compare figure
41.
THE TELENCEPHALON IN CYCLOSTOMES
403
Fig. 40 Diagram of the relations of functional columns drawn on the outline
of the Lampetra brain. The visceral receptive column is shaded by oblique lines,
the somatic receptive column by vertical lines. The primordium hippocampi
is cross-hatched with oblique lines and it is evident that it is the caudal portion
of the column devoted to olfactory and gustatory functions. The lower border
of the cross-hatched area in the figure is the sulcus limitans hippocampi, both rostral and caudal to the interventricular foramen.
404
J. B. JOHNSTON
Fig. 41 Diagram similar to that of figure 40, drawn on the outline of the brain
of Squalus acanthias. Drawn from the bisected brain. Owing to the somatic
receptive area being situated on the lateral surface of the telencephalon, its projection on this figure overlaps the olfactory area. The medial sulcus limitans
hippocampi is marked by a wavy line along the lower border of the primordium.
This figure illustrates the U-shaped flexure of the visceral receptive column, the
attachment of the olfactory peduncle at the base of the U , and the position of the
somatic receptive area between the two limbs of the U . The axis of the brain
ends in the recessus praeopticus and the great forebrain flexure involves only the
dorsal columns.
CONTRIBUTION'S FROM THE ZOOLOGICAL LABORATORY OF THE MUSEO.U OF COMPARATIVE ZOOLOGY AT
HARVARD COLLEGE, NO. 234
THE NUMERICAL RELATIONS OF THE HISTOLOGICAL
ELEMENTS IN THE RETINA OF NECTURUS
MACULOSUS (RAF.)
SAMUEL C. PALMER
TWELVE FIGURES
CONTENTS
I. Introduction 405
II. Historical review 407
A. Retina 407
B. Optic nerve 411
III. Material and technique 412
A. Material 412
B. Technique 413
IV. Observations 417
A. Measurements 417
a. Retinal layers 417
b. Cross-sections of the optic nerve 419
B. Enumerations 420
a. Visual cells 420
b. Outer nuclear layer 423
c. Ganglionic layer 424
d. Mailer's fibers 425
e. Inner nuclear layer 427
f . Optic nerve fibers 429
V. Discussion 431
VI. Theoretical considerations 436
VII. Summary 438
Bibliography 439
I. INTRODUCTION
Although the vertebrate eye has long attracted the attention
of investigators and has been the subject of numerous researches,
few attempts to enumerate the histological elements of the retina
and of the optic nerve have been made. The exceedingly delicate nature of the retina has always been a serious difficulty
in the way of its histological study, but with the introduction
405
THE JOURNAL OF COMPARATIVE -VEUROLOOY, VOL. 22, NO. 5
OCTOBER, 1912
406 • • . SAMUEL C. PALMER
of Golgi's bichromate method and of Ehrlich's methylene-blue
method for staining nervous tissues, this difficulty has been,
at least partially, overcome, and as a result great advance has
been made in our knowledge of the visual apparatus. We owe
much, also, to the use of osmic acid, which has been so successfully employed, not only in the study of the finer structure of
nerve cells and their processes, but also in the enumeration of
nervous elements. In the optic nerve this has not always been
satisfactorily carried out, because the fibers of this nerve are
very small and difficult to stain. The usual treatment has been
to blacken the medullary sheaths with osmic acid, which, however,
leaves the axis-cylinders unstained.
Many theories have been elaborated to explain the structure
and functions of the retinal elements, but where the numerical
relations of these units have been concerned investigators have,
for the most part, confined their enumerations to regions of
special interest, leaving untouched the broader aspect of the
entire retina and optic nerve. It has seemed to me, therefore,
that a complete enumeration of the histological elements of the
retina and of the optic nerve, which have to do directly with the
transmission of visual impulses, would be a desirable addition
to our knowledge of the eye; and I have, therefore, undertaken
to complete such an investigation on one of the lower vertebrates.
There is great similarity in the structure of the retina in all
classes of vertebrates. From the standpoint of the neurone
theory, the visual apparatus in these animals consists of three
distinct layers of neurones. These neurones bear so constant
a relation to one another that a definite terminology has become
associated with them. The first neurones to receive the visual
impulses are the visual cells, which include the rod-and-cone
layer, a majority of the nuclei in the outer nuclear layer, and
processes terminating in the outer reticular layer. The second
set of neurones is represented by the nuclei of the inner nuclear
layer exclusive of Miiller's fibers and are of two distinct forms,
viz., amacrine cells and bipolar cells. Processes from the latter
form synapses with similar processes arising from the visual and
from the ganglion cells. The third set of neurones consists of
HISTOLOGICAL ELEMENTS RETINA NECTURUS 407
the ganglion cells, which are described by Ram6n y Cajal ('94)
as sending free branching processes into the inner reticular layer,
and axis-cylinders to the central organ through the optic stalk.
My problem is concerned with enumerations of the rods, cones,
and double-cones, and the nuclei associated with them, of the
nuclei of the inner nuclear layer, and the ganglion layer, of the
Miiller's fibers, and the fibers of the optic nerve.
All my investigations have been made in the Zoological Laboratory of Harvard University under the personal supervision of
Prof. G. H. Parker, to whom I am greatly indebted for advice
and valuable criticism.
II. HISTORICAL REVIEW
A. Retina
Although the literature on the retina and optic nerve in vertebrates is extensive, it is surprising that so little has been done
on the numerical relations of the retinal elements. For the most
part, those who have investigated the retina in this respect have
limited their statements to the fovea and to comparisons between
the number of visual and ganglioh cells in central and peripheral
regions. An epitome of the morphology and physiology of the
retina has been published by Greeff ('00), but it is not satisfactory
for numerical relations of the elements because of the lack of sufficient data.
Much of what has been written concerning the number of
retinal elements in mammals relates to the human retina. One
of the earliest to consider the question was Krause ('76), who
estimated the number of rods in the human retina to be 130,000,000 and of cones to be 7,000,000. Salzer ('80) also worked on
the human retina and estimated the number of cones to lie between 3,000,000 and 3,600,000, but gave no estimate of the number of rods or of other retinal elements. Foster ('91) and many
other physiologists have apparently accepted the estimates of
Salzer. In regard to the distribution of the rods and cones Foster
writes Over the retina (including the ora) the rods are much
more numerous than the cones, there being two or three rods
408
SAMUEL C. PALMER
in the line joining two cones/' and Toward the extreme periphery of the retina the cones become more numerous and close
to the ora are alone present." Hesse ('00) gives the total number
of visual cells in the human retina as 50,000,000. Stohr ('06)
believed that the rods were more numerous than the cones and
that the latter occurred at regular intervals, so that three or four
rods lay between adjacent cones. Putter ('02) has given a great
deal of attention to enumerations of the histological elements
in the retina and in the optic nerve of marine mammals. The
total number of elements in the different layers of the retina
was found to be enormous (table 1). Estimates of the number
of rods ranged from 227,000,000 in the adult Phoca vitulina to
800,000,000 in Macrorhinus leoninus and Balaenoptera physalus.
As no mention was made of cones, except in the case of Hyperoodon rostratus, where they were said to be wanting, the retinas
were presumably pure rod retinas. The nuclei in the outer nuclear layer were said to be from six to thirteen times as numerous
TABLE 1
Estimated numbers of retinal elements and optic nerve fibers in certain species of
marine mammals (after Putter, '02)
NUMBER OP RODS
PER SQUARE
MILLIMETER
MAXIMUM NUMBER OP RODS IN
RETINA
NUMBER OF NUCLEI PER
SQUARE MILLIMETER IN
NUMBER OF OPTIC
NERVE FIBERS
Outer
nuclear
layer
1,250,000
1,367,000
1,512,500
722,000
2,000,000
550,000
1,350,000
794,000
918,000
Inner
nuclear
layer
Per 1
meter
fc a o
« "^
Macrorhinus
leoninus
Phoca barbata .
Phoca vitulina. .
Odobaenus
rosmarus
Otaria jubata
Balaenoptera
ph}\salus
"Phocaena communis
90,000
120,000
110,000
110,000
250,000
62,000
200,000
150,000
111,000
800,000,000
303,000,000
227,000,000
256,000,000
475,000,000
800,000,000
175,000,000
735,000,000
557,000,000
110,000
119,000
78,000
82,000
181,000
62,000
184,000
98,000
90,000
103
68
74
62
74.
13
29
28
15
767,000
174,000
147,000
111,000
140,000
157,000
30,100
137,000
77,000
1:1050
1:2086
1:1544
1:2300
1:2000
1:5095
1-4850
Dclphinapterus
leucas. . . .
1 :5560
Hypcroodon
rostratus
1:7200
HISTOLOGICAL ELEMENTS RETINA NECTURUS 409
as the rods, which would make the enormous total for the outer
nuclear layer in Phoca barbata more than 4,000,000,000 nuclei.
In all the species mentioned in table 1, the number of nuclei in
the inner nuclear layer approached more closely that of the rods,
being slightly less in most cases. Equally important is the comparatively small number of optic nerve fibers associated with
this enormous number of retinal cells. Putter estimated that
in Balaenoptera physalus there were only 13 optic nerve fibers
per square millimeter, giving a total of 157,000 for the entire
nerve. In this case there would be about 5000 visual cells to
a single optic nerve fiber. Considerable difference was found
between the number of elements in embryonic and adult retinas.
As a rule the nuclei were more abundant in the former.
Investigation into the numerical relations of the retinal cells
in other mammals, though meagre and fragmentary, indicate a
condition similar to that in man. Chiarini ('06) expressed in a
general statement concerning the visual cells of the dog, the unsatisfactory condition in which we find this problem in mammals,
when he said, "The cones are less numerous than the rods."
Franz ('09) has given a definite enumeration of the numerical
relations of the retinal elements for the central and peripheral
regions of the retina in birds. The nuclei were found in eight
species to be more numerous at the center than at the periphery.
In the fundus of the retina of Motacilla alba there were on a
line 0.1 mm. in length 266 nuclei in the inner nuclear layer, 60
in the outer nuclear layer, and 50 in the ganglionic layer; but
over the same distance at the periphery there were only 40 nuclei
in the inner, 20 in the outer, and 4 in the ganglionic layer. To
find the total number in one square millimeter, Franz multiplied
these numbers by 10 and squared the product. On this basis
the fundus was stated to have in Motacilla 250,000 gangUon
cells and 360,000 rods and cones, in Bubo 36,000 ganglion cells
and 78,400 rods and cones to a square millimeter.
I have been unable to find any enumerations of the retinal
elements of reptiles. It is important to note, however, that the
so-called rods are said to be wanting in some species. Thus
Ram6n y Cajal ('94) says, In die Retina der Eidechse die Stab
410 SAMUEL C. PALMER
chen fehlen." The number of elements involved is probably
greater in eyes of equal size in reptiles than in amphibians,
because of the larger size of the elements in the latter.
Detailed enumerations of retinal elements in amphibians have
not been made, so far as I can learn, but Howard ('08) estimated
that the rods, cones, and double-cones in the retinas of Necturus
based on estimates in the fundus, were in the relation 4:1:1
respectively; but he made no mention of his method of obtaining
this result. The outer nuclear layer is said by him to consist
of a single layer of nuclei in the fundus and a double layer at
the periphery, each rod and each cone is described as having a
nucleus and each double-cone, two nuclei. Schultze ('67) beheved
that there was only one nucleus to each double-cone.
Franz ('05) has found the number of nuclei per square millimeter in the outer nuclear and ganglionic layers in the number
of selachians. The nuclei, in most cases, were found to be more
numerous about the center than at the periphery. In Acanthias
blainvilli the number of nuclei in the outer nuclear layer near
the center of the retina was 24,000 per square millimeter and in
the ganglionic layer in the same region 1200; in Galeus galeus
near the center there were 75,000 nuclei to a square millimeter
in the outer nuclear layer and 1500 in the ganglionic layer. In
the deep-sea selachians there was a great increase in the number
of nuclei in the outer nuclear layer and a decrease in the ganglionic layer. Thus, in the fundus over an area of one square
millimeter there were in the retina of Chimaera monstrosa 100,000
nuclei in the outer nuclear layer and only 600 in the same area
in the ganglionic layer.
Enumerations of the visual elements in the eyes of invertebrates have been made in some cases. Parker ('90) placed the
number of facets in an adult lobster's eye at 13,500 and ('95)
the number of ommatidia in the eye of an adult crayfish (Astacus)
at 2500. Hesse ('00) estimated that there were between 2100
and 2400 rods in the eye of Pecten jacobaeus. Among cephalopods, the retina of Loligo was said to contain 162,000 rods per
square millimeter and of Scaeurgus only 26,000, with other species
ranging between the two.
HISTOLOGICAL ELEMENTS RETINA NECTURUS 411
B. Optic nerve
Estimates of the number of optic nerve fibers, have been confined chiefly to the optic nerve of man. Kuhnt ('75) found 200
fibers in the diameter of the optic nerve of a new-born child,
and 220 to 240 in that of a man forty years old, giving totals of
approximately 31,400 and 40,000 respectively for the entire crosssections. Krause ('76) put the number at 1,000,000 at least,
but later ('80) reduced it to 400,000 including both large and
small fibers, and an equal number of very small fibers. Salzer
('80) also worked on the optic nerve of man and from three nerves
obtained an average of 437,745 fibers.
The only important contribution, to which I have had access,
relating to the number of optic nerve fibers in amphibians is a
short paper by Lauber ('02), who counted 450 fibers in a crosssection of the optic nerve of Cryptobranchus japonicus.
Among invertebrates Parker ('95) determined that seven
fibers were connected with each ommatidium in the crayfish eye.
This gave a total of 8085 retinal fibers in the case of a young
crayfish and 16,625 in an old one. Proximal to the fourth optic
ganglion these totals were reduced to 2021 fibers in the former
and 4156 in the latter.
It is a generally credited theory that the majority of the optic
nerve fibers originate in the retina and pass centripetally along
the optic stalk to the brain, and that a smaller number arise in
the brain and pass centrifugally to the retina. This view has
the support of such investigators as His ('90), Ramon y Cajal
('91) and Robinson ('96). On the other hand Balfour ('81)
did not hold this view, believing rather that the fibers of the
optic nerve were derived from a differentiation of the epithelial
cells of which the nerve was at first formed.
The axis-cylinders of the optic nerve in a majority of vertebrates are small and medullated. In some amphibians, viz.,
urodeles, the optic nerve was described by Osborn ('88) as 'greatly
reduced,' and in some examples of Necturus there was stated to
exist, in the adult condition a persistent lumen which opened into
the T-\ike expansion of the third ventricle of the brain. Kings
412 SAMUEL C. PALMER
bury ('95), likewise, describes the optic nerve of Necturiis as
hollow for a portion of its length and states that its fibers are
entirely amyelinic. This latter condition is said by Edinger
('92) to be the case in the young of certain other amphibians.
After a careful survey of all the Uterature at hand bearing on
the numerical relations of the histological elements of the optic
nerve and retina, I have failed to find for any vertebrate a consistent enumeration of these elements which has been carried
out in such a way as to give reasonably safe grounds for comparisons. I have, therefore, undertaken this task in reference to
Necturus.
III. MATERIAL AND TECHNIQUE
• A. Material
It has long been known that the retinal elements in amphibians are very large as compared with those in other vertebrates.
Howard ('08) gives the dimensions of the outer and inner segments
of the rods in several species of amphibians as follows: In the
outer segment the length varied from 24:/x in Triton to 76/i in
Bufo, and the width from 6m in the frog to 12u in both Triton
and Salamandra. The outer segments of the rods in Necturus
are said to be 36 to 40^ long and 12// wide. Measurements
made by myself on the diameter of the cones of Necturus just
distal to the ellipsoids averaged 4.8m, and through the ellipsoids,
where visual cells first come in contact with neighboring visual
cells, they averaged lO/i. The diameters of the rods through
the ellipsoids was slightly larger than that of the cones. Slonaker
('97) states that "Amphibia have not only long rods, but the
thickest found in vertebrates." In speaking of the cones, he
says, they have the greatest diameter in mammals." Table
2 shows the relative sizes in micra of the rods and cones in representatives from all classes of vertebrates. The length of the
elements is non-essential for my purpose, but the diameter is
of especial significance because it is one of the most important
factors in determining the number of elements which can occupy
a given space, when they are crowded together as are the visual
cells in the vertebrate retina. From the measurements quoted
HISTOLOGICAL ELEMENTS EETINA NECTURUS
413
it will be seen at once that, because of the large diameter of the
visual cells, the number of these elements in a given area will
be fewer in the amphibia than in any other class of vertebrates.
The two conditions, viz., large diameter and fewer elements,
unite to make the amphibian retina especially favorable for a
study of the numerical relations of the constituent parts. With
this point in mind I have selected for my investigation the adult
form of Necturus maculosus (Raf.), the common 'mud-puppy'
of the fresh water streams and lakes of eastern Canada and of
middle and southern United States (Cope, '89). The specimens
were secured by the Zoological Department from Venice, Ohio.
Comparalive sizes of the outer segments of rods and cones in representatives of the
different classes of vertebrates (after Muller '56)
DIMENSIONS IN MICRA OF THE OUTER SEGMENTS OF THE
SPECIES EXAMINED
Rods Cones
Diameter
Length Diameter
Length
Man
Pigeon
Chameleon
Frog
Perch
1.5 - 1.8
2.6 - 3.3
6.0 - 7.0
2.6
40.0-60.0 4.0-6.0
20.0-28.0 i 1.0-5.0
1.0 - 1.3
40.0 - 60.0 5.0
40.0 - 50.0 !
1
32.0 - 36.0
25.0 - 30.0
60.0 - 80.0
20.0 - 28.0
8.0 - 12.0
Upon their arrival at the laboratory they were transferred at
once to a fresh-water cement aquarium in a dimly lighted part
of the basement of the Museum of Comparative Zoology, where
they were easily kept in a healthy condition.
B. Technique
I have found that the technique usually employed for the
retina does not give satisfactory results when applied to the optic
nerve; for this reason I have been obliged to make separate preparations for the two structures.
In order to secure material for a reliable enumeration of the
retinal elements, a fixation fluid was necessary which would not
wrinkle the retina, and at the same time could be followed by
414 SAMUEL C. PALMER
successful double staining, to which I shall refer later, whereby
small fragments of rods could be distinguished from bits of cones.
The large size of all the retinal cells in Necturus has been a great
aid in the identification, and in the accuracy of the counts, of
the separate elements of the retina. The most successful results were obtained by fixation in Kleinenberg's picro-sulphuric
mixture. My method was as follows : Live animals were placed
in a bowl of tapwater in which a few small crystals of chloretone
had been dissolved as a means of preventing the discharge
of slime (Cole, '02). Chloroform was then added gradually
until the animals were thoroughly anesthetized. The eyes were
quickly removed and placed in picro-sulphuric acid, care being
taken to free them from as much superfluous tissue as could be
done quickly. To keep the orientation, a piece of skin was left
attached to the dorsal side of the eyeball, differences in shape
of the pieces serving to distinguish right and left eyes. I found
the pieces of skin useful also in orientating the eyes in paraffin.
The best results were obtained by immersing the unopened eyeballs in the picro-sulphuric mixture for four or five hours. They
were then rinsed in distilled water a few minutes and dehydrated
by passing them gradually through 35 per cent, 50 per cent, 90
per cent, and 100 per cent alcohol over a period of two days.
When the eye was sufficiently hardened (90 per cent alcohol),
the front face was cut away with a sharp razor, and the lens
removed. Early in my work I found that the heat of a paraffin
bath, extending over a time sufficient to insure saturation with
paraffin, caused considerable shrinkage of the sclera and wrinkling of the retina. I, therefore, followed Biitschli's chloroform
method of de-alcoholization. Transfer from the chloroform-paraffin mixture of this method to hard paraffin was completed by
the evaporation of the chloroform over a water bath at about
60°C. and a five minute immersion in hard paraffin melting at
about 56°C.
Sections S/j. thick were made in one set of eyes parallel to the
antero-posterior^ plane of the eye and passing through the optic
1 The terms 'anterior,' 'posterior,' 'dorsal' and 'ventral' as applied to the eyefjall in this account, arc used in the sense of coniijarative anatomy; i.e.. 'anterior'
HISTOLOGICAL ELEMENTS RETINA NECTURUS 415
nerve, and in another set parallel to the dorso-ventral plane,
and passing through the optic nerve. Series of sections 6^ thick
were made through the entire thickness of the retina tangential
to the surface of the eyeball in the anterior, posterior, dorsal,
and ventral regions and in the fundus. The sections were stained
in Heidenhain's iron haematoxylin as a base, and in a 70 per
cent alcoholic solution of eosin as a counter stain. Thirty minutes
in the mordant (2 per cent ferric alum) and one hour in the haematoxylin gave very satisfactory results. The excess of stain
was washed out in ferric alum of the same strength as the mordant, and the washing was continued until all traces of the haematoxylin had disappeared from the outer segments of the rods
and from the reticular layers. At this stage the nuclei of the
outer and inner nuclear layers and of the ganglionic layer were
clearly defined and light blue in color. The nuclei of Miiller's
fibers were stained a deep blue to blue-black and contrasted
sharply with the fighter blue of the surrounding nuclei. Control
was kept over the process of destaining by examining the slides
every few seconds under the microscope. Two minutes in the
counter-stain were sufficient to color the outer segments of the
rods bright red. The outer and inner reticular layers appeared
as broad red fibrous bands separating the inner nuclear layer
from the outer nuclear and the ganglionic layers, respectively.
The strands of Miiller's fibers, which stretched radially outward
from the internal limiting membrane, were stained an intense
red. It is clear that the selective qualities of the stains employed
rested primarily with the haematoxylin, for in the process of
reducing the over-stain of the base the outer segments of the
cones, the nuclei of MuUer's fibers, and the ellipsoids, retained
their color longer than the other elements, thus indicating their
greater chemical affinity for the basic stain. Although the success which attended fixation in picro-sulphuric acid and double
staining with haematoxylin and eosin made other methods superfluous, nevertheless some entirely successful preparations were
refers to that part of the eyeball which is nearest the anterior end of the animal
('internal' in human anatomy), 'dorsal' to that part which is nearest the dorsal
midline ('superior' in human anatomy), etc. The deep part of the eyeball, often
called the posterior part, is here referred to as the 'fundus.'
416 SAMUEL C. PALMER
made with the use of other reagents. Both the vapor of 2 per cent
osmic acid and vom Rath's picro-osmo-platinic-chloride-acetic
mixture gave excellent preservation of the retinal elements,
though the outer segments of the rods and cones were over-blackened. Good preservation and successful double-staining were
obtained by fixation in either Perenyi's fluid, Fol's mixture, or
7 per cent nitric acid, followed as before with haematoxylin and
eosin stains.
I have already called attention to the non-medullated character of the optic nerve fibers in Necturus, hence the usual fixation fluids in which osmic acid is used to stain the medullary
sheaths are ineffective for the optic nerve fibers, in this animal.
Vom Rath's fluid gave excellent preservation of the supporting
and vascular tissues, but was unsatisfactory for the nerve fibers.
Ranson's ('09) modification of Ramon y Cajal's silver-nitrate
method for non-medullated nerve fibers was tried without success. With another modification of this method, that of Mullenix
('09), I succeeded in staining the fibers, but the definition was
poor. The only method tried which brought out the fibers distinctly was a modified form of Bielschowsky's ('03) method. In
order to secure the necessarily rapid fixation of the proximal
portion of the optic nerve, I cut away the tissues surrounding
the skull, which was then split at both anterior and posterior
ends. This permitted the formaUn to enter the brain cavity
quickly. The non-medullated fibers when impregnated by this
method appeared in longitudinal section as sharply defined
somewhat undulatory, brownish-black to black lines. In crosssection (figs. 10, 11, 12) they were irregular black spots or streaks
in a yellowish-brown matrix. Dehydration and de-alcoholization were carried out as with the retina. Cross-sections of the
optic nerve 5m thick were made close to the chiasma and as near
as possible to the eyeball.
The results obtained with Bielschowsky's fluid have justified
its use in this case. There is no doubt in my mind that the irregular black spots and streaks referred to above are nerve fibers.
I was fortunate in having a longitudinal section of an optic nerve
turn up slightly so that the fibers could be seen to end as small
HISTOLOGICAL ELEMENTS RETINA NECTURUS 417
black spots of different sizes. In a longitudinal section individual
fibers could be traced only a short distance. At the distal end
they spread out in bundles along the inner margin of the retina
and disappeared radiating outward between the nuclei of the
ganglionic layer. I was wholly unable to detect a union between
the ganglion cells and the optic nerve fibers, and I am unable
therefore to state the exact relation of the optic nerve fibers to
the retinal elements.
IV. OBSERVATIONS
A. Measurements
a. Retinal layers. The eyeballs of Necturus lie well forward
on the dorso-lateral aspect of the head, where they appear as
slightly arched whitish bodies. They are unusually small for
the size of the animal, and are approximately spherical in shape.
The retina, which is closely applied to the sclera, has, therefore,
the shape of a zone of one base whose area is only slightly less
than that of a hemisphere. Since the area of a zone of one base
is equal to the area of a circle whose radius is the chord of the
generating arc, the area of the retina in Necturus is equal to the
area of a circle whose radius is the shortest distance from the
periphery of the retina to the center of its fundus. To obtain
this center I made a camera drawing ( X 101) of a median section
of the eye, and erected a perpendicular at the middle point of
the chord joining the ends of the retina at the ora. The point
of intersection of the perpendicular and the retina marks the
center required. The chord joining this center to the periphery
is equal to the radius of a circle whose area is that of the zone
of one base, which marks the limits of the retina. In many cases
the center lay directly in the optic nerve, while in nearly all the
remaining eyes, it lay very close to that nerve. By this method
I have calculated the minimum, maximum, and average areas
of zones of one base (which hereafter I shall refer to as zones)
for 14 retinas, the three zones coinciding with the external limiting membrane, the middle part of the inner nuclear layer and
the middle of the ganglionic layer (fig. 1, cd, xz, vw). The results
418
SAMUEL C. PALMER
of my measurements are given in table 3. Eight retinas were
measm^ed in the antero-posterior and six in the dorso-ventral
plane. Variations in the thickness of the retinas (figs. 2 to 4),
measured from visual cells to internal limiting membrane, and
irregularities of the retinas, especially at the periphery, are the
causes of the differences of area in retinas nos. 3 and 8, 5 and 6,
and 10 and 14.
In order to enumerate the retinal elements, it was necessary
to adopt unit areas small enough to avoid the distortion at the
margin of the microscopic field and large enough to include a
great number of elements. Convenient sizes were found in a
circular area of 0.013 sq. mm. for the visual cells and one of 0.0078
sq. mm. for the other elements. The areas of the retina in the
zones at the different levels were duly considered, so that the
number of visual cells and nuclei of the outer nuclear layer was
TABLE 3
Calculated areas of zones corresponding to the area of the retina in Necturus arid
passing through (1) the external limiting membrane, (2) the middle of the inner
nuclear layer, and (3) the ganglionic layer
AREAS OF ZONES IN SQUARE MILLIMETERS AT THE
DESIGNATION
PLANES OF SECTIONS
External limiting
Middle of inner
Middle of the
membrane
nuclear layer
ganglionic layer
1
Antero-posterior. .
12.5664
11.7094
10.9073
2
Antero-posterior. .
13.4484
11.8309
10.3138
3
Antero-posterior . .
15.1777*
13.5815
12.0693
4
Antero-posterior. .
13.8940
12.2255
10.6535
5
Antero-posterior. .
15.0399
13.6455
12,3176
6
Antero-posterior. .
1 15.0399
13.8940
12.8165
7
Antero-posterior. .
12.0693
10.9133
9.8120
8
Antero-posterior. .
15.1777*
14.0721*
13.0690*
9
Dorso-ventral —
14.6303
12.1947
9.9743
10
Dorso-ventral
10.8184t
9.7028t
8. 69161
11
Dorso-ventral
12.5664
11.4616
10.4257
12
Dorso-ventral
13.2541
11.8005
10.4257
13
Dorso-ventral
j 13.9602
12.3796
10.9073
14
Dorso-ventral —
10.9351
9.7569
8.6916t
Average areas
of zones in square
millimeters
13.4698
12.0834
10.7910
- Maximum areas
t Minimum areas
HISTOLOGICAL ELEMENTS RETINA NECTURUS 419
based on an area obtained for the zones at the external Hmiting
membrane; Miiller's fibers and gangUon cells for the zone through
the ganglion layer; and nuclei for the inner nuclear layer from
the area of the zone passing through the middle of this layer.
The number of unit areas in each zone was found by dividing
the number of square millimeters in the zone by the number of
square millimeters in the unit area. The total number of elements
in a layer obviously equaled the product of the number of areas
into the number of elements per unit area. The methods employed for the other layers were evidently unsuited for enumerations of the inner nudear layer, for in this layer we have to do
with solid content rather than surfaces. For this layer I have
resorted to counting the nuclei in a cylinder with a head of 0.0078
sq. mm. and with its long axis placed radially. The length of
the cylinders was determined by the number of microtome sections necessary to pass completely through the layer, the number
of sections being eight in each of the two cases -counted. The
number of such cjdinders was found by dividing the area of the
zone of the inner nuclear layer by the area of the cylinder head.
In all cases where elements touch the boundaries of the unit
areas (figs. 5 to 9) they were rated at one-half their value within
the field.
b. Cross-sections of the optic nerve. The areas of the crosssections of the optic nerve varied according to their location
(figs. 10 and 11). In all cases examined the nerve was very much
smaller proximally than distally, in one instance the former
amounting to little more than one-third the latter (table 15).
My method of calculating the cross-sectional areas of the nerves
was modelled after that employed by Parker ('95) on the optic
nerve of Astacus. Camera drawings of all the sections to be
measured were made on paper of uniform thickness and weight;
these were then cut out and weighed. A standard unit 0.0015
sq. mm. of the same magnification was also cut out and weighed.
I could then easily obtain the required areas from the arithmetical formula:
X o: Y when T is constant
where X equals the area of the cross-section, Y equals the weight
420 SAMUEL C. PALMER
of the drawing, and T equals the thickness of the paper. In
sections near the chiasma allowance was necessarily made for the
lumen of the stalk, which becomes obliterated distally.
B. Enumerations
a. Visual cells. The sections used in enumerating the visual
cells were cut tangentially to the surface of the retina in the five
regions already referred to, passing through the outer segments
of the rods and cones, and through the paraboloids of the doublecones (fig. 1, ah). The visual cells, therefore, were seen in crosssection, and because of their structure, large diameter, and differential staining qualities they were easily distinguished from one
another. I was unable to detect any plan in the arrangement
of the rods and cones, such as Schwalbe ('87) has depicted, but
noted a marked tendency for five or six elements of a kind to
run in lines, a feature which I think is without real significance.
The associatiorl of rods or cones in groups of six or eight, (figs.
6 and 8) was of frequent occurrence. Their usual distribution
may be described as irregularly scattered, and free from contact
along their outer segments with neighboring elements (figs. 5 to 9).
With a magnification of 615 diameters the cross-sections of the
rods were bright red, circular to oval in outline, and with the
characteristic vacuolated structure described by Howard ('08).
They were larger than the cones and somewhat more numerous.
The cones appeared as small round, blue-black, homogeneous
bodies scattered irregularly over the field; the double-cones were
far less numerous and much larger than either the rods or the
cones. As one should expect, the paraboloids were fused along
one side (figs. 5 to 9), giving the appearance of double-elements.
Their structure was reticular and took the stain only slightly. In
addition to the elements already mentioned, there were a few
whose identity could not be established with certainty, due, I
think, to disintegration having set in before they were reached
by the fixative fluids. They constituted only a very small percentage of the total number of visual cells.
Studies of the cross-sections of the cells in the five regions
described, showing the close relation between the number of
rods, cones, and double-cones, in the different positions, are
HISTOLOGICAL ELEMENTS RETINA NECTURUS
421
clearly set forth in table 4. I have taken the averages from five
retinas in each case, right and left eyes being used indiscriminately. Twenty eyes were used, and in five cases counts from
two different regions of the same eye were made, and in two
cases right and left eyes from the same animal were considered.
Averages per unit field for the right and left eyes respectively
show a slightly greater number of rods and cones, and a smaller
number of double-cones and doubtful elements in the left eye.
These differences are shown in table 5. The maximum and
minimum counts are, however, so close in every case as to lead
me to believe that the oiumber of elements involved in right and
left sides is approximately the same, and I shall therefore make
no discrimination between the two.
TABLE 4
Number of rods, cones, double-cones and uncertain elements in unit areas
of 0.013 sq. mm.
REGIONS OF THE EYEBALL IN WHICH THE UNIT AREAS WERE LOCATED
DESIGNATION
OF
EYEBALLS
Anterior
Posterior
Dorsal
Ventral
Fundus
R*
C
D
X
R
C
D
X
R
C
D
X
R
C
D
X
R
C
D
X
7r
46.0
39.5
12
1
81
70.5
49.5
14
56.5
47.5
14
1
16 r
2U
35.0
44.5
21
42.5
41.0
14
2
52.5
46.5
14
4.0
22 1
23 r
49.2
41.0
14
2
41.0
37
17
23 Z
65.5
28.5
10
6.0
37.5
31
16
24 r
50.0
26
20
2
24 {
25 1
66.0
42.5
25
64.0
42.0
8
9.5
26 r
28 r
47.5
47.0
14
59.0
37.5
19
1
50.5
37.0
12
1
Sir
43.0
42.5
15
4
70.5
43.0
5
4.0
ZZl
45.0
49.5
18
2.5
38 r
56.0
29.5
12
iOl
48.0
54.0
10
1
56 r
43.5
38.0
14
57 r
59 r
55.5
41.5
25
42.5
36.5
10
0.5
601
40.6
28.0
8
3
Average ]
of 5
57.9
41.9
15.8
0.4 48.2
43.1
17.8
0.4
43.6
41
11.8
1.9
59.5
41.9
11
5.2
46.2
36.2
15.8
0.8
retinas ,
- R, rods; C, cones; D, double- -sones; X, uncertain elements; r, right eye; /, left eye.
THE JOURNAL OF COMP.\RATIVE NEUROLOGY, VOL. 22, NO. 5
422
SAMUEL C. PALMER
From tables 4 to 7 it will be seen that the rods are generally
more numerous per unit field than the cones and double-cones.
Exceptional cases exist, however, where the cones are found
to be more numerous than the rods (table 4, nos. 16 r, 33 I, 40 I),
and I am convinced after examination of a great number of retinas
that such areas are not infrequent in every one of the five regions.
The actual relative values of rods, cones, and double-cones and
the total average number per unit fields, as well as the total average
number per five unit field, are given in table 6, where the rods
consistently outnumber the cones. In table 7 I have brought
together many data for the visual cells. Between the maximum
and minimum retinas there is a variation of 25 per cent, at least,
in the total number of visual cells.
TABLE 5
Average number of retinal elements per unit area in right and left eyes
K
a
m m
AVERAGE NUMBER OF
MAXIMUM NUMBER OP
MINIMUM NUMBER OF
tj
+5
T1
SIDE EXAMINED
•z. «
fl
c
3
go
3
3
3
11
< «
.
0.ii
O *i
ii
K 5
S2
S3
^2
S2
J3 t.
^2
S2
■n a)
^03
g«a
o n
^ta
gw
o a
§ta
§«a
rt
U
P
tf
O
P
«
O
Right
0.013
49.2
38.2
15
70.5
47
25
35
26
5
Left
0.013
53
41.7
12.7
70.5
49.5
25
37.5
28
8
TABLE 6
Averajge numbers of visual cells in the five selected unit areas {see table 4)
POSITIONS OF UNIT FIELDS
AVERAGE NUMBERS OF THE SEVERAL KINDS OP
RETINAL ELEMENTS PER UNIT AREA IN THE
FIVE REGIONS OF THE EYE
AVERAGE
NUMBER OF
ELEMENTS PER
Rods
ri„„„„ DoubleC°°«« cones
Uncertain
elements
UNIT AREA
Anterior
57.9
41.9
15.8
0.4 .
116.0
Posterior
48,2
43.1
17.8
0.4
109.5
Dor-sal
43.6
41.0
11.8
1.9
98.3
Ventral
59.5
41.9
11.0
5.2
117.6
Fundus
.46.2
36.2
15.8
0.8
99.0
Total number of the several
kinds of elements in five
fombined unit areas
255.4
204.1
72.2
8.7
540.4
HISTOLOGICAL ELEMENTS RETINA NECTURUS
423
To correlate the number of visual cells with the number of
nuclei in the outer nuclear layer, it was necessary to count each
double-cone as two units, on the assumption that each doublecone has two nuclei. This view is held by Howard ('08), who
found two nuclei associated with each double-cone in macerated
material. My own observations on sectioned material confirm
this relation. The proportions of rods to cones and to doublecones approximates 3.5 : 2.8 : 1, respectively, which is a decided
increase in the relative number of cones over that given by
Howard.
b. Outer nuclear layer. The outer nuclear layer, when examined in radial sections of the eye (figs. 1 to 4) was seen to consist
of a complete single external row of nuclei with here and there
additional nuclei lying directly against its inner side. In calculating the number of nuclei in the 'external' sheet of which
the 'single row' is the section, I have used the method already
employed for the visual cells. The numbers of nuclei per unit
area in the external sheet are given in table 8. In the fundus
the numbers are slightly less than in the other regions. In order
to include the partial 'internal' sheet in my enumerations, I
counted the nuclei in the external and internal rows in median
sections from periphery to periphery in eight retinas. In the
TABLE 7
Total numbers of visual cells in retinas of minimum, maximum, and average sizes.
The enumerations are based on the following average numbers of elements in a unit
field of 0.065 sq. mm. area: rods, 255.J^; cones 204.1; double-cones, 72.2; uncertain
elements 8.7; total visual cells, 540.4 {table 6)
RELATIVE SIZE
OF EYEBALLS
CALCULATED ARE;
RETINAS IN SQT
MILLIMETERS Al
TERNAL LIMIT
MEMBRANE (T
3)
NUMBER OF UNIT
FIELDS IN RETU
TOTAL NUMBER OF
Rods
Cones
Doublecones
Unceitain
elements
Visual
cells
Minimum . . .
Maximum ....
10.8184
15.1777
166.437
233.503
42,508
59,637
33,970
47,658
12,017
16,859
1,448
2,032
89,943
126,185
Average of 14
retinas...... 13.4698 207.228
52,926
42,295
14,962
1,803
111,986
424
SAMUEL C. PALMER
external row there was an average of 422 nuclei, as compared
with 121.1 in the internal row. Since the nuclei of the two layers
have the same average diameters in the plane tangential to the
surface of the eyeball, the ratio of the number of nuclei in the
external layer to the number in the internal layer is 422 : 121.
The total number of nuclei in each of these layers as well as in
the whole outer nuclear layer is given in table 9. By comparing
tables 7 and 9, the number of nuclei in the outer nuclear layer is
seen to exceed the number of visual cells by about 10 per cent; or, if
directly compared for total numbers of elements, there are 121,000
nuclei in the outer nuclear layer to 111,000 visual cells.
c. Ganglionic layer. The nuclei of the ganglionic layer, which
in radial sections of the eye (figs. 1 to 4), are seen to be a single
TABLE 8
Number of nuclei of the outer nuclear layer per unit area of 0.0078 sq. mm.
DESIGNATION OF
REGIONS OF THE EYEBALL IN WHICH THE FIELDS WERE LOCATED
Anterior
Posterior
Dorsal
Ventral
Fundus
1 r*
81
16 r
21 r
211
22 1
23 r
231
24r
241
25 r
25 1
26 r
28 r
31 r
32 r
38 r
30 1
40 r
40 1
51.5
60
42
58.5
49
53.5
60
60
59
62
59
61
53
60.5
56
51.5
42.5
57
51
71.5
55.5
54
49
47
43
Averages of 5
retinas
52.2 58.9
57.9
54.7
•19.7
"r, right eye; I, left eye.
HISTOLOGICAL ELEMENTS RETINA NECTURUS
425
layer thick, are larger, more rounded and less closely grouped
than are the nuclei of the other retinal layers. Sections from
the five visual regions (table 10) in five retinas show as before a
shght variation in the average number of nuclei per unit area,
but this I believe is due to accidental conditions and is not at
all consequential. Contrary to the condition found in the outer
nuclear layer, the number of nuclei in the ganglionic layer is
greater in the fundus than elsewhere. In table 11 the average
number of nuclei per area of 0.39 sq. mm. is given as 111.1
and the total number of nuclei in a retina of average size is
about 30,000.
Thus we see that in passing centripetally through the layers
of the retina there is a gradual decrease in the number of elements
composing each layer, except in the inner nuclear layer, so that
according to the views usually expressed, visual impulses arising in a number of visual cells are transmitted to the central
organ over a greatly reduced number of elements.
d. Mailer's fibers. Miiller's fibers were counted to best advantage in tangential sections through the inner reticular layer close
to the ganglion-cell layer, where they appeared as intensely red
spots in a net-work of small light-red fibers. They occurred in
pairs and triplets as well as singly (figs. 1 to 4) . I have assumed
that each fiber represents a cell with a nucleus lying generally
in the inner nuclear layer. Shght variations in the number of
TABLE 9
Total numbers of miclei of the outer nuclear layer in retinas of minimum, maximum,
and average sizes
fe W A O W
>j
.J
O K >< g; J
■<
ffl-i w 5 9
■^ t= ^ H ^
m ^
^
^
K f; g
b «
ft. «
fe B 0!
H C?"< „ f"
S o
t E
S ^ H
g
o m
O g W
RELATIVE SIZE
OF EYEBALLS
« to 00 g
g tog , 5
■< !0
P OS OH 9
■« ^ ri
§2
a ph
S S
w 5
s2
(a s- "^
O H S H W^
" J H
0b,
RAGE
UCLEI
ELD I
^EET
Z « H
, J H
Z H H
, J J
■J o o
<
^«s tlss?
gSP
^ Z fc 0!
g^" 1
g^S
gzz;
o
^
-i
f \
H
H
Minimum
10.8184
0.039
277.394
273 A
75,840 1
21,764
97,604
Maximum ....
15.1777
0.039
389.172
273.4
106,400
30,558
136,958
Average of 14
retinas
13.4698
0.039
345.379
273.4
94,427
27,097
121,524
426
SAMUEL C. PALMER
TABLE 10
Numbers of the miclei of the ganglionic layer per unit area of 0.0078 sq. vnn.
DESIGNATION OP
REGIONS
OF THE EYEBALL IN WHICH THE FIELDS WERE
LOCATED
Anterior
Posterior
Dorsal
Ventral
Fundus
7r*
31.5
9r
19.5
16 r
25.5
21 r
14
16.5
21 /
19
22/
23
23 r
23
23
23/
16
24 r
27.5
24/
16.5
33.5
26r
18.5
26.5
28 r
18.5
30/
13,5
31 r
25
31 /
20
32 r
25
24
33/
20
38 )•
18
40 r
25.5
40/
32.5
Averages of 5
retinas
18.0
24.8
21.6
19.7
27.0
- r, right eye; /, left eye.
TABLE 11
Total numbers of nuclei of the ganglionic layer in retinas of minimum, maximum,
and average sizes
fc, H H JL, H
fc, H
o e ■< J J
- ^
%t'^%<
OS J
IS P
fa o
W (?«<-?,
■* s
H H
C i;
K to H o
z S
« <
'^ Z H 6, «
Sm
p«
SE
a^ a
HF.LATIVE SIZE OF
a - « o S
X. »
^ 55
P3 b. U
EYEBALLS
'h 5 H « ^
s 2
o£
g25
•< z " J
ii. a K
S W m
J, W J
P H -J c
J « S a On
III
p "
pi
■5 D z
gzo
8.6916
0.039
55
■<;
H
Minimum
222.861
111.1
24,760
Maximum
13.0690
0.039
335.102
111.1
37,230
Averages of 14
retinas
10.7910
0.039
276.723
111.1
30,744
I
HISTOLOGICAL ELEMENTS RETINA NECTURUS
427
fibers per unit area occurred, but not sufficiently great to call
for more than passing notice. In table 12 I have given the average numbers of fibers per unit area and the average numbers
for five retinas in each of the selected regions. The fibers were
counted in unit areas, in some cases in right and left eyes of the
same animal, and in others in two regions in the same eye; but
I could detect no characteristic differences. In table 13 the
average number of fibers in five unit areas is given as 97.5 and
the total number in the whole retina is betw;een 21,729 and 32,672.
e. Inner nuclear layer. The inner nuclear layer presents in
Necturus a variable condition, which makes it, of all the retinal
layers, the most difficult in which to count the nuclei. It con
TABLE 12
Number of Muller's fibers per xmit area of 0.0078 sq. mm.
DESIGNATION OP
EYEBALLS
REGIONS
or THE EYEBALL IN WHICH THE UNIT AREAS WERE LOCATED
Anterior
1 Posterior
Dorsal Ventral
Fundus
77
21
8r
21
16 r
24
17 1
24
21 r
18
13
211
17
16
23 r
21
13
24 r
21
241
22.5
20
25 1
13
26 r
22
28 r
15
30 1
16
31 r
20.5
311
19
32 r
24
33 1
21
38 r
20
22 1
19.5
40 r
18
40 1
27
Averages of 5
retinas
19.1
20.9
18.0
/
21.3 1 18.2
r, right eye; I, left eye
428
SAMUEL C. PALMER
TABLE 13
Total numbers of Muller's fibers in retinas of minimum, maximum, and average sizes
relative size op
eyeballs
CALCULATED AREAS OP
RETINAS IN SQUARE
MILLIMETERS AT
MIDDLE OF GANGLIONIC LAYER (table
3)
ir; IS
<
In inner nuclear layer
exclusive of
Miiller's
fibers
JO
J" C3
3 2
o
a ^ ■<
5 «
z ^ ■>■
9.7028
14.0721
1243.948
1804.115
121
121
142
142
131
131
141.228
203,667
21,729
32,672
162,957
236,339
Averages of 14 retinas
12.8034
1549.153
121
142
131
175,959
26,980
202,937
/. Optic nerve fibers. As I have already said, the optic nerve
was transected in two planes, viz., near its two ends, and the
difference in the cross-sectional areas in these two regions was
clearly established. When the fibers in the two regions were
studied, those in the proximal portion seemed smaller and slightly
more numerous to a unit area than in the distal portion. This
led me to suppose that the total number of fibers was less proximally than distally, and my opinion was borne out by actual
counts in the two regions in two optic nerves. Examination
of other optic nerves indicated that similar numerical relations
of the fibers existed in the two regions and was a characteristic
feature of the optic nerve of Nee turns. All counts were made
on cross-sections of the optic nerves. Outline camera drawings
( X 755) were made of cross-sections together with the nuclei
430
SAMUEL C. PALMER
of the supporting tissue, all the largest fibers, and all the prominent markings of the optic nerve carefully sketched. The drawing was then marked off with coordinating lines and the rest of
the optic nerve fibers were drawn in place and counted. By
practice in counting I was able to make out and record the fibers
in the sections with accurac} and speed.
I have counted the fibers in three of the nerves given in table
15 twice each. The results of the second counts were in each
case so close to the first counts that I did not think it necessary
to continue the process for every nerve; thus, in nerve no. 1 (fig. 12)
I counted 2001 fibers on the first trial and 2003 on the second;
in nerve no. 2, 1657 fibers on the first count and 1661 on the second;
TABLE 15
Areas of cross-sections of optic nerves and numbers of nerve fibers counted at different
planes of transection
DESIGNATION OF
NERVES
CALCULATED AREA IN SQUARE MILLIMETERS OF CROSS-SECTIONS OF THE
OPTIC NERVE
TOTAL NUMBER OF FIBERS IN
CROSS-SECTIONS
Close to eye
Close to chlasma
Close to eye
Close to chiasma
1
2
3
4
5
0.017
0.019
0.019
0.026
0.027
0.008
0.009
2002
1659
1780
1858
2613
853
1071
and in nerve no. 5, 2616 fibers on the first count and 2611 on the
second. The number of fibers appearing in table 15 for these
optic nerves are averages obtained from the two counts. The
complete results of my enumerations, together with the areas
of the cross-sections of the optic nerve, are given in table 15.
The average area near the eye was 0.0216 sq. mm. and contained
by actual count an average of 1982.4 fibers or about 92,000 per
square millimeter; the average of the cross-sections near the
chiasma was 0.0085 sq. mm. with an average of 962 fibers, or
approximately 113,000 per square millimeter. Although the
proximal portion of the optic nerve is smaller in diameter than
the distal part, it is, on the other hand, seen to be richer in fibers
per unit area.
HISTOLOGICAL ELEMENTS RETINA NECTURUS 431
V. DISCUSSION
My intention in this investigation has been, as far as possible,
to make a consistent enumeration of all the nervous elements
in the retina and optic nerve in a single species of animal, and I
have believed the logical choice of species to be some animal
whose retinal cells are very large and few in number. Such an
animal was naturally sought among the amphibians, and especially among those species whose eyes and optic nerves have undergone reduction in size, probably through diminished functioning
powers, and whose histological elements were well known to be
of unusual size. In Necturus I have found an animal in which
both eyeballs and optic nerves are reduced in size; the retinal
elements are extremely large, if not the largest known; and the
optic nerve fibers are entirely non-medullated.
The nearly spherical shape of the eyeball in Necturus and the
close application of the retina to the sclera have made the measurements of the retina comparatively easy and have led, I believe,
to accurate results. The method employed has been described
on page 417. The individual retinal cells are so large and free
from contact with one another that I have been able to count
and number the individual cells in each unit area. Following
this the application of the unit area to the area of the retina has
been a matter of simple mathematical calculation.
An attempt to estimate the total number of visual cells in the
retina of Necturus by counting the rods, cones, and double-cones
in a median section of the eye extending from periphery to
periphery gave a total of 143,000 visual cells for an average sized
retina. This number exceeds that found by the method finally
adopted by about 31,000 cells or 28 per cent. Since in the latter
method every element per unit area was counted and averages
obtained as already stated, and the number of areas in a given
retina is not subject to variation, I am convinced that the number
of retinal cells in Necturus is close to the number obtained by
this means, and that the method of counting elements in a line
as a basis of enumeration of the visual cells should be rejected
on the ground that it gives too large a number of cells.
432 SAMUEL C. PALMER
Where the retinal cells are very small and numerous the difficulties of obtaining accurate counts are greatly increased. Hess
('05) has demonstrated in the retinas of Eledone and Sepia the
great variation which exists in the number of visual cells in closely
approximated regions in the same retina, and thereby implies
the impossibility of obtaining reliable estimates of the total number of visual cells in a retina from the number in a given 'belt.'
It is commonly believed that the retinal cells in vertebrates
are not evenly distributed over the retina. Franz ('05, '09)
states that the visual cells are more numerous about the fundus
than near the periphery; Howard ('08) calls attention to the double
layer of nuclei near the periphery in the outer nuclear layer in
Necturus; and my own observations on the same species show a
slight variation in the numbers of the different elements in the
different regions. Consequently I believe that estimates based
on counts in a restricted region, as for example, the fundus, or
the periphery, give no fair idea of the number of elements in the
retina as a whole, and my observations show that estimates
based on counts of elements in a line of definite length exaggerate
the number of cells in a given retina. Nor can I accept Putter's
('02) method, viz., that of computing from the diameter of a
rod the number of visual cells that may be found in a square
millimeter and in the retina as a whole. Figs. 4 to 9 show that
in Necturus the interstices between the visual cells make up a
large portion of the area of a zone passing through the outer
segment of the visual cells, and these spaces must be considered
in the retinas of all species of vertebrates. Without consideration of these spaces the number of elements obtained would greatly
exceed the actual number present.
In order to avoid, then, what appear to me to be errors of method, I have taken great care to secure accurate counts per unit
area in a number of regions of the retina in several animals.
The retina of Necturus lends itself to a count of this kind, because
the visual cells, the external sheet of the outer nuclear layer,
Miiller's fibers, and the ganglion cells are each represented by
a single layer of nuclei.
HISTOLOGICAL ELEMENTS RETINA NECTURUS 433
The fovea, when present in the amphibian retina, is small.
I have not been able to find it in Necturus, and Howard ('08)
makes no mention of such a 'spot,' but Hulke ('67) and Chievitz
('91)- have seen it in Triton and Salamandra. The frequent
grouping of 6 to 8 cone cells (figs. 5 to 9) in different parts of the
retina of Necturus may, perhaps, compensate for the absence
of a definite fovea.
Enumerations of nuclei in the outer nuclear layer (tables 8
and 9) bring out several important features. On the ground that
each visual cell has its own nucleus there should be in the outer
nuclear layer a number of nuclei equal to the number of rods
and cones together, unless elements of another kind should be
found in either or both the layers compared. The nuclei of the
outer nuclear layer were found to outnumber the rods and cones
by about 10,000. Undoubtedly a majority of the nuclei in the
internal layer together with all those in the external layer should
be associated with the visual cells; but there is a characteristic
group in the internal layer, having their long axes at right angles
to the long axes of the nuclei of the visual cells, which appear to
me to have a different function. They may, perhaps, be horizontal cells, which Ramon y Cajal ('94) states are represented in
amphibians by large and small nuclei at two different levels and
constitute the outermost part of the inner nuclear layer. There
are, too, in the internal layer a small number of Miiller's-fiber
nuclei (fig. 4) whose identity is clearly established by their heavy
stain and fibers. A fourth kind of nucleus may occasionall}'
wander into this layer. Fig. 2 shows how the outer limits of
the inner nuclear layer may be thrown out of line and individual
nuclei be protruded far into the outer reticular layer. This
would seem to favor Bernard's ('00) contention that the nuclei
of the retinal layers are constantly migrating outward to aid in
the formation of new elements in the more outwardly lying layers.
I have been able to observe an apparent migration of this kind
only in the case cited.
Conditions in the inner nuclear layer show that it is the most
variable of all the layers in respect to the number of its elements.
2 See Slonaker, 1897.
434 SAMUEL C. PALMER
I have called attention to the three-layer condition of its nuclei
as the most characteristic condition, but two or four layers were
not uncommon. Ramon y Cajal ('94) points out that the inner
nuclear laj'er of amphibians consists of a number of 'types' of
both amacrine and bi-polar cells, but I have made no attempt in
this study to distinguish between them, .and have considered
the layer merely as a whole. Though the results obtained cannot
be adapted to every retina because of the great individual variation, I am convinced that they are as accurate as possible for the
three-layered average sized zone.
The ganglion-cell layer presents few features of special note
in connection with the number of its nuclei. It consists uniformly
of a single layer of loosely associated, large nuclei. A consideration of vital importance is the failure of Bielschowsky's impregnation method to demonstrate a union between the ganglion
cells and the optic nerve fibers. Just what the real significance
of this is, I am unable to say, and, when considered in relation
to the number of optic nerve fibers in proximal and distal parts
of the optic nerve, the interpretation becomes even more difficult.
Enumerations of the cross-sections of the strands of Miiller's
fibers per unit area in the inner reticular layer gave better results
than enumeration of their nuclei per unit area in the inner nuclear
layer, because at the plane of sectioning in the reticular layer
there is no other structure with which the} might be confused;
secondly, the fibers stand out clearly in cross-section, and each
fiber may be supposed with reasonable certainty to represent
a complete unit; and, lastly, the chance of missing even a single
fiber in the unit areas, was very small.
The objections to using the nuclei as a means of enumeration
lie in the difficulty of distinguishing the nuclei of Miiller's fibers
from other nuclei in the layer; and secondl}^, in the fact that
the nuclei of Miiller's fibers are not always found within the
limits of inner nuclear layer (fig. 4), in which case it would be
impossible to count with certainty all the cells in a given field.
Enumerations of the optic nerve fibers were more tedious than
difficult. The black ends of the fibers contrasted sharply with
HISTOLOGICAL ELEMENTS RETINA NECTURUS 435
the surrounding tissues. Over-blackened margins and the apparent fusion of occasional fibers did not prove to be insurmountable
difficulties, for by focusing, the separate fibers could usually
be distinguished, so that I believe the number of fibers counted
in a cross section is very close to the actual number present.
In addition to variations in diameter in a given nerve, there
are also individual variations which are considerable. Measuremerits near the chiasma are fairly uniform, but at the distal end
of the nerve I found a range in area of 62.9 per cent. The number
of fibers here correlates in some degree with the cross-sectional
areas of the nerves. Thus in table 15, nerve no. 2, with a crosssectional area of 0.019 sq. mm. has an average of 1659 fibers,
and nerve no. 5, with an area of 0.027 sq. mm., has an average of
2613 fibers.
The number of fibers in other nerves than the optic nerve of
Necturus have been counted or estimated in some instances.
From Salzer's ('80) calculations there are between 60,000 and
70,000 fibers per square millimeter in the human optic nerve;
Birge ('82) has counted 3550 fibers per square millimeter in the
7th spinal nerve of the frog, and 14,133 in the 10th; Hatai ('03)
found a variation in the number of fibers in the spinal nerves
of the white rat according to the position of the plane of transection, there being more in the proximal than in the distal planes,
which is the reverse of the condition in the optic nerve of Necturus; Donaldson and Bolton ('91) record an average of 11,900
fibers to every square millimeter in the dorsal roots of the spinal
nerves of man; Dunn ('00) has found that the total number of
fibers innervating the hind foot of the frog is between 5000 and
6000; and on page 430 I have shown that in the optic nerve of
Necturus there are about 100,000 fibers per square millimeter.
Thus we see that, although in general the visual apparatus
of Necturus is described as degenerate, and the animal's habits
have apparently brought about a reduced functional activity
of the visual cells, the optic nerve appears to have more nerve
fibers per unit area than any other nerve so far studied.
436 SAMUEL C. PALMER
VI. THEORETICAL CONSIDERATIONS
Theoretical consideration of the optic functions is not the primary object of my investigation, and I shall enter into it only so
far as my research indicates exceptional conditions in Necturus.
I have found in the visual cells that rods and cones alike develop
at the extreme margin of the retina, the initial element being
indifferently a rod or a cone. Since this is so, whatever differences there may be in the light perceiving potentialities between
central and peripheral regions, they must depend largely on the
degree of the functional development of the visual cells in these
regions. The presence of rods and cones alike over the whole
retina — if the theory that rods are organs for light and shadow
perception and cones for color preception is true — indicates
power to distinguish colored lights as well as light and shadow
at the periphery as well as in the fundus. In this connection
Reese ('06) found that Necturus responded to both red and blue
lights, but since no analysis of the lights for purity of color or
intensity was made, it is not evident to what the reactions were
due. Pearse ('10) has shown that Necturus reacts readily to
ordinary light stimuli through both the eye and the skin. From
these investigations it appears that Necturus is capable of distinguishing colored as well as white light, but on this point there
is need of further investigation.
I know of no positive evidence that horizontal cells exist in
the retina of Necturus, but I know of no other explanation for
the group of cells referred to on page 423 (figs. 2 and S, n). The
arrangement of the nuclei in the inner nuclear layer seems to
me to preclude the existence of such cells in that layer. Since
I have already shown that the nuclei of Miiller's fibers may migrate or be pushed outward in some way from the inner nuclear
layer into the outer nuclear layer, it is possible that a similar
change in position has taken place with the horizontal cells, and
that in time they have become permanent constituents of the
outer nuclear layer. Investigation into the identity of these
cells by Golgi's, or some other stain equally valuable for nerve
processes, is very desirable.
HISTOLOGICAL ELEMENTS KETINA NECTURUS 437
Because of the great variability of the inner nuclear layer, I
cannot help wondering what the influence of such variation may
be on the sight of the animals. Can animals with five layers
of cells in this region see better than those with two? Or does
the number of cells involved have no 'effect whatever on the
clearness of vision?
Enumerations of the optic nerve fibers in cross-sections of
the optic nerve show that distally there are nearly double the
number of fibers that there are in the proximal portion; a condition which suggests at once a dichotomous division of the axiscylinders. Such an interpretation of the increase of the fibers
distally would mean that a majority of the optic nerve fibers in
Necturus have their origin in the brain, which is the reciprocal
of the condition found by His ('90), Assheton ('92), and Robinson
('96) in other vertebrates. But Robinson also states that the
optic nerve fibers arise in the retina and are more numerous near
the retina even when the fibers have come to occupy the entire
length of the optic stalk. The implication is that some of the
fibers fail at this stage to reach the central organ.
In my treatment of the optic nerve of Necturus with Bielschowsky's fluid, I have been unable to demonstrate a morphological
connection between the ganglion cells and the optic nerve fibers,
but the fibers seem to pass between the nuclei of the ganglion
cells and enter the inner reticular layer. If the fibers can in any
way be shown to be joined to the ganglion cells, then we should
have in the adult Necturus a condition similar to that found by
Robinson in the embryos of higher vertebrates.
Since a direct union, then, between the optic nerve fibers and
the ganglion cells is not an established fact, the origin of the
fibers is a matter of speculation. Do the fibers originate wholly
in the brain and pass centrifugally to the retina, branching within the optic nerve and ending freely in the retina? Or do they
have their origin chiefly in the retina, in spite of the facts that
staining with Bielschowsky's fluid fails to show positive connection between the ganglion cells and the fibers, and that only a
half of them reach their destination in the brain? In consideration of these questions the influence of the degeneracy of the
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 6
438 SAMUEL C. PALMER
eye, and the fallibility of the stain must be given due weight.
I am unwilling to make any statement as to the origin of the
optic nerve fibers in Necturus, and await with interest further
investigation of this subject by other methods.
VII. SUMMARY
1. The proportion of rods to cones is about the same in all
regions of the retina. Double-cones are wanting at the extreme
periphery.
2. There is no particular plan of arrangement of the visual
cells.
3. In the retina of average size there are about 110,000 visual
cells, of which 53,000 are rods, 42,000 cones, and 15,000 doublecones.
4. The total number of visual cells varies with the size of the
retina. In maximum sized retinas the number of visual cells
is about 126,000; in minimum sized retinas, about 90,000.
5 . The number of visual cells is less than the number of nuclei
in the outer nuclear layer.
6. The total number of nuclei in the outer nuclear layer in
an average-sized retina is 121,000. The number varies from
137,000 in maximum sized retinas to 97,000 in mimimum sized
retinas.
7. The outer nuclear layer consists of two sheets; an external
complete, and an internal loosely scattered sheet, with 94,000
and 27,000 nuclei, respectively, in the average-sized retinas.
8. The nuclei of the internal sheet of the outer nuclear layer
consists of nuclei of the visual cells, of Miiller's fibers, and possibly of horizontal cells.
9. The inner nuclear layer is the most variable of all the layers
in the number of its elements. In an average sized retina there
are approximately 176,000 nuclei in a layer composed of three
sub-layers. The range in the number of nuclei in maximum and
minimum retinas of this structure is 204,000 to 45,000.
10. The inner nuclear layer may have as many as five sublavers or as few as two.
HISTOLOGICAL ELEMENTS RETINA NECTURUS 439
11. Nuclei of Miiller's fibers lie chiefly in the inner nuclear
layer, but a small number may be found in the outer nuclear layer.
In an average sized retina there are about 26,734 of these nuclei,
the maximum and minimum numbers being 33,000 and 22,000,
respectively.
12. The number of ganglion cells in the smallest retina measured, was 24,758; in the largest, 37,229; and in an average-sized
retina 30,464.
13. The optic nerve of Necturus varies in diameter with the
plane of transection. Near the chiasma its cross section has
on the average an area of 0.0085 sq. mm., and an average of 962
nerve fibers; near the eyeball the average area of the cross section
is 0.0216 sq. mm., with an average of 1982 nerve fibers.
14. The proportion of histological elements of the retina and
optic nerve are approximately as follows: visual cells 111, nuclei
in the outer nuclear layer 121, nuclei in the inner nuclear layer,
exclusive of Miiller's fibers, 175, ganglion-cell nuclei 30, Miiller's
fibers 26, optic nerve fibers distally 2, optic nerve fibers proximally 1. .
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440 SAMUEL C. PALMER
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HISTOLOGICAL ELEMENTS RETINA NECTURUS 441
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Salzer, F. 1880 Ueber die Anzahl der Sehnervernfasern und der Retinazapfen
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EXPLANATION OF FIGURES
The drawings are all from Necturus maculosus (Raf.) All the outlines in figs1 to 12 were made with the aid of the camera lucida. The sections of the retina
were stained in Heidenhain's iron haematoxylin followed by a 70 per cent alcoholic solution of eosin. Radial sections of the visual cells (figs. 1 to 4) were cut
8m thick, and cross-sections (figs. 5 to 9) 6^ thick.
The optic-nerve fibers were stained in Bielschowsky's fluid in every case, and
all sections were 5ju thick.
Fig. 1 Semi-diagrammatic drawing of a radial section of a normal retina of
Necturus; cd, xz, viv designate three zones in which the areas of the retinas were
obtained; ah, mn, xz and vw designate the 'levels' in which average counts, per
unit areas, were obtained for the different layers of the retina. X 331.
Fig. 2 Semi-diagrammatic drawing of a radial section of a retina with two
sublayers or 'sheets' in the inner nuclear layer, n, horizontal cell. X 331.
Fig. 3 Semi-diagrammatic drawing of a radial section of a retina with four
to five sublayers in the inner nuclear layer, n, horizontal cell. X 331.
Fig. 4 Semi-diagrammatic drawing of a radial section of a retina with two
nuclei, m, of Midler's fibers, in the outer nuclear layer. X 331.
442
0.
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o
o
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8
c
i)\j
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Figs. 5 to 9 Seini-diagrammatic drawings of cross-sections of tin; visual cells
in five regions of the retina. Fig. 5, anterior; fig 6, posterior; fiK. 7, fundus; fig. 8,
dorsal; fig. 9, ventral; r, rod; c, cone; cd, double-cone. X 282.
Fig. 10 8emi-diagnimmatic drawing of a cross-section of the optic nerve
(no. 4, table 15) near the eyeball. X 431.
Fig. 11 Semi-diagrammatic dm wing of the same ojjfiit nerve near the chiasma.
0, lumen of the nerve. X 431.
Fig. 12 Semi-diagrammatic drawing of a cross-section of nerve (no. I, table 15)
near the eyeball. X 485.
444
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11
12
445
ON THE HISTOLOGY OF THE CRANIAL AUTONOMIC
GANGLIA OF THE SHEEP
F. W. CARPENTER
From the Zoological Laboratory, University of Illinois, under the direction of
Henry B. Ward, No. 19
TEN FIGURES
Both anatomical and experimental methods of investigation
have established the fact that the autonomic nervous system of
vertebrates consists, on its efferent side, of two sets of neurones.
The first of these, the preganglionic neurones, have their cellbodies in the central nervous axis, and send their neurites outward
by way of the ventral roots of cerebio-spinal nerves to the autonomic ganglia. In the trunk region these preganglionic fibers
pass from the spinal nerves in the white rami communicantes
to the ganglia of the sympathetic trunks, or to ganglia more
distally placed. In the cranial region, preganglionic fibers leaving the brain by the third, seventh and ninth nerves end in the
ciliary, sphenopalatine, otic, submaxillary and sublingual ganglia,
which constitute the autonomic ganglia of the head.
The efferent nervous impulses which thus reach outlying ganglia of the body are carried onward to peripheral tissues (involuntary muscle, glands) by the postganglionic neurones. These are
multipolar nervous elements, the cell-bodies of which lie in the
autonomic ganglia. Their distally directed neurites are in mammals, as a rule, nearly or quite devoid of myelin.
By employing modern methods of neurological technique, such
as those introduced by Golgi, Ehrlich and Cajal, it has been
possible to demonstrate very satisfactorily the nature of the endings of the preganglionic fibers in the autonomic ganglia of the
trunk region. These ganglia, according to the terminology proposed by Langley, belong to the sympathetic and sacral subdivi
447
448 F. W. CARPENTER
sions of the autonomic system. The histological investigations
of Aronson, Retzius, Dogiel, Huber and others on various vertebrates have led to the general conception of such endings as pericellular, intracapsular networks of fine fibrils, surrounding and
in contact with the cell-bodies of the postganglionic neurones.
These end nets are not to be confused with the intercellular fibers,
often intertwined and concentrically arranged about the cellbodies of the ganglia, but situated outside the cell capsules. Such
fibers include the long extracapsular dendrites of the sympathetic
cells, their non-medullated neurites, and the collaterals and terminal portions of the preganglionic fibers before the latter penetrate the cell capsules to give rise to the subcapsular nets.
Our knowledge regarding the terminations of preganglionic
fibers in the cranial autonomic ganglia is, with the exception of the
ciliary, less complete. In the ciliary ganglion pericellular nets
under the capsules have been observed by a number of investigators. Michel ('94) and Kolliker ('94) were the first to call
attention to their presence following the study of Golgi preparations of mammalian ganglia. Recently Sala ('10) and v. Lenhossek ('10), working with the Cajal silver nitrate method, have
been able to secure excellent demonstrations of these end nets in
the ciliary ganglia of man. That they are present also in birds
has been shown by v. Lenhossek ('10, '11) and the writer (Carpenter '11), both of whom found, however, that in this group
another form of termination of the preganglionic fibers occurs in
the ciliary ganglion. This is the calyx" ending and its modifications. Endings of this type have been seen also in the ciliary
ganghon of reptiles by v. Lenhossek ('11a).
The histology of the remaining autonomic ganglia in the head
region has received comparatively little attention from investigators.
Original descriptions of the cellular elements of the sphenopalatine ganglion are to be found, as far as I am aware, in three papers
only, and in but one of these are the terminations of preganglionic
fibers mentioned. The observations of Retzius ('80) on teased
preparations of the ganglion taken from the sheep and cat furnished for a long time the only source of information regarding
CRANIAL AUTONOMIC GANGLIA OF SHEEP 449
its minute structure. Retzius found the cells mostly multipolar,
with some bipolar elements in the cat. His method did not permit the study of nerve terminations in the ganglion. In 1894
V. Lenhossek described Golgi preparations of the sphenopalatine
ganglion of the mouse, and gave us the only account of fibrillar
end baskets around the ganglion cells. In the recent paper of
Mliller and Dahl ('10) a good description is given of the morphology of the cells of this ganglion in the horse, sheep, and man,
but no mention is made of intracapsular end nets. The method
of Bielschowsky was used. In one preparation (human) a pericapsular 'Nervenfasernetz' was observed by them, from which
terminal' fibers appeared to run to the cell-body. This will be
referred to later.
In the otic ganglion the terminations of preganglionic neurones
have not been demonstrated. The literature dealing with the
histology of this ganglion is, in fact, very meager. Retzius ('80)
ascertained from teased preparations that the ganglion contained
multipolar cells in the rabbit, cat, sheep and man. Mliller and
Dahl ('10) have confirmed this, by means of the Bielschowsky
method, for the horse, sheep and man.
The cells of the closely related submaxillary and sublingual
ganglia have been described as multipolar elements by Retzius
('80), Huber ('96) and Miiller and Dahl ('10). Huber alone saw
pericellular end nets. These were observed in Golgi preparations
of the ganglia from young dogs.
METHODS
The nerve terminations described in this paper were demonstrated by means of intra-vitam staining with methylene blue.
The sheep's heads were brought to the laboratory about an hour
after the animals had been killed, and injected through the
carotid arteries with a 1 per cent solution of methylene blue in
distilled water. The blood vessels were washed out before and
after the staining by injections of Ringer's solution. Both this
and the methylene blue solution were used at approximately body
temperature.
450 F. W. CARPENTER
After the ganglia desired for study had been dissected out, they
were fixed over night in a 10 per cent sohition of ammonium
molybdate, then washed in running water, dehydrated in grades
of alcohol, cleared in xylol, and embedded in paraffin. The
sections were cut from 25 to 50 micra in thickness.
For comparison, preparations of the otic ganglion were made
by the silver nitrate method of Ramon y Cajal. These were
of some value in showing the form of the ganglion cells and
their processes, but in them the terminal end nets were not
differentiated.
OBSERVATIONS
In this investigation attention has been directed chiefly to the
endings of the preganglionic fibers on the cell-bodies of the postganglionic neurones. In using methylene blue intra-vitam staining
to demonstrate nerve terminations it has been found that the
treatment of the ganglia in such a manner as to differentiate these
clearly usually leaves the cell-bodies, about which the endings are
arranged, partially or wholly unstained. On the other hand, when
the cell bodies and their processes are deeply colored, the endings
of the preganglionic fibers are almost always invisible. It follows,
therefore, that the majority of my preparations are not suitable
for the study of the morphology of the postganglionic neurones.
There occur, however, here and there in the sections, ganglion
cells sufficiently well stained to warrant giving some account of
their structure.
The postganglionic neurones
In the sphenopalatine, otic and submaxillary ganglia of the sheep
the cells are multipolar in character, with long, slender, sometimes
branching dendrites, which penetrate the cell capsule, and often
run for surprising distances among the intercellular fibers. Such
cells are shown in figures 1, 2 and 3. The boundaries of the cell
capsules are marked by dotted lines, except in figure 2, where
the position of the capsule is indicated by several of its nuclei.
Among the processes given off by the cell-bodies, I have often
found it difficult to distinguish the neurite from the dendrites.
CRANIAL AUTONOMIC GANGLIA OF SHEEP 451
In figure 1 the fiber marked A appears to be the neurite, in this
instance arising from a dendrite. It may be traced through the
thick section in which it occurs for the distance of nearly one-half
a millimeter from its origin. It joins a bundle of fibers lying
along the surface of the ganglion. Throughout its length, as far
as it can be followed, it remains non-medullated.
Preparations of the otic ganglion stained by the Cajal silver
nitrate method also show that the cells of this ganglion are multipolar; and, moreover, that some of them are fenestrated, resembling in this respect certain ciliary ganglion cells of mammals
and birds (Sala, v. Lenhossek) and certain spinal ganglion cells
of mammals (Cajal).
The ganglion which has proved most refractory in revealing
the character of its cells is the ciliary. Here no cells with long,
slender processes, such as those of the other ganglia, have been
brought to light by methylene blue in the six ganglia examined
by this method. In most cases no processes at all are apparent,
but occasionally a cell showing a single thick, branching, extracapsular dendrite (fig. 4) has been observed. Whether such
cells are numerous in the sheep's ciliary ganglion, or occur sporadically only, I cannot say. It would be unsafe to make the latter
deduction merely because a partial and capricious stain like methylene blue shows them in comparatively few numbers.
Schwalbe ('79, '79 a ) described the cihary ganglion cells of the
sheep, studied by the isolation method, as unipolar. In other
mammals (cat, dog, monkey) they have been shown to be multipolar by Sala ('10) and Marinesco, Parhon and Goldstein ('08),
who employed the method of Cajal. In some instances the dendrites extend beyond the cell capsules, in others they are short and
intracapsular. The latter condition seems to be the rule in the
ciliary ganglion of man.
It appears, then, that the autonomic cranial ganglia of the
sheep contain cells which are allied in their morphological characters with those of the mammalian sympathetic ganglia. Both
are characterized by long dendrites which penetrate the cell
capsules. In the possession of these extracapsular dendrites,
however, the cranial cells of the sheep differ from the elements of
452 F. W. CARPENTER
corresponding ganglia in human beings. In man, as Sala ('10) and
V. Lenhossek ('10) have shown for the cihary, and Miiller and Dahl
('10) for the remaining autonomic cranial ganglia, as well as the
ciliary, the dendrites are contained within the cell capsules. They
are often bent and branched, and may run paiallel with the surface of the cell-body for considerable distances, but they do not,
as in the sheep, break through the capsular wall.
TJiQ terminations of preganglionic fibers
In the ciliary, sphenopalatine, otic and submaxillary ganglia
of the sheep the preganglionic fibers terminate in end nets of fine,
varicose fibrils embracing the cell-bodies of the postganglionic
neurones (figs. 5, 6, 7, 8, 9, 10). These end nets lie inside the cell
capsules, and are at places in direct contact with the surfaces of
the cell-bodies. We have, therefore, in the cranial autonomic
ganglia essentially the same conditions in respect to synapses that
obtain in the vertebral and prevertebral ganglia of the sympathetic subdivision of the system. Here the presence of subcapsular end nets has been shown by a number of investigators, notably
by Huber ('99), who succeeded in differentiating these terminations with methylene blue in all classes of vertebrates from fishes
to mammals.
When examined in detail under high powers of the microscope,
the pericellular plexuses are seen to arise through the terminal
branching of one or more preganglionic fibers. The largest number observed was four in the ciliary ganglion (fig. 5) . Such fibers
perhaps result from the division of a single preganglionic neurite,
or they may be the terminal portions or collaterals of two or more
distinct neurites. In all cases the fibers are non-medullated near
the end nets, but when the conditions are favorable for following
them, they may be traced, in the opposite direction, into bundles
of fibers with thin medullary sheaths.
The fibrils of which the pericellular plexuses are composed
show many varicosities. These vary in size and are distributed
irregularly along the course of the fibrils. Sometimes they are
terminal in position, i.e., they occur at the tips of short free-ending
CRANIAL AUTONOMIC GANGLIA OF SHEEP 453
branches, as is well shown in figure 6, A. The varicosities and
intermediate portions of the fibrils are often in direct contact'
with the surface of the cell-body, but they are also found in the
space between the latter and its surrounding capsule.
The pericellular plexuses are veritable networks. Anastomoses
between the fibrils are frequent, and at the nodes varicosities
usually occur. This reticulate condition can be accounted for
consistently with the outgrowth doctrine of the development of
nerve fibers by assuming that the growing preganglionic neurite,
on reaching the postganglionic cell-body, divides tree-like into
a number of terminal fibers. These embrace the cell-body on all
sides, and, meeting with one another here and there, fuse to form
the continuous network.
Although all the end nets are of essentially the same character
in the autonomic cranial ganglia of the sheep, they vary in complexity. In the same ganglion one may observe such comparatively simple endings as are shown in figures 8 and 10, and such
complete and intricate networks as those of figures 6 and 9. In
the drawings only the fibrils and varicosities on the upper sides
of the cell-bodies have been represented. By focussing through
the transparent ganglion cells the continuations of the nets may
usually be seen on the surfaces away from the observer.
In my experience with methylene blue used according to the
injection method the end nets of the sphenopalatine ganglion
have proved the most difficult to stain satisfactorily. Very frequently the varicosities have been colored a deep blue without
affecting the delicate fibrils which connect them. The result
gives to the cell-body enclosed by the net a peculiar, spotted
appearance. Figure 7 represents a pericellular plexus of the
sphenopalatine ganglion in which many of the communicating
fibrils are invisible, although some of the varicosities on their
course have taken the stain.
In the introductory references to the literature dealing with
cranial autonomic ganglia mention was made of the pericapsular
' Nervenf asernetze ' demonstrated through Bielschowsky staining by Miiller and Dahl ('10) in a single preparation of the sphenopalatine ganglion of man. These bundles of intertwining fibers
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 5
454 F. W. CARPENTER
are concentrically arranged about the capsules oi the ganglion
'cells. From them a few centrally directed offshoots ending in
knobs are traceable through the capsular wallg to the surfaces of the
underlying cell-bodies. That these extracapsular, nest-like structures are not identical with the intracapsular end nets described
above is clear from their position, and the inter-relations of their
fibers, which do not appear to anastomose. They are doubtless
bundles of preganglionic neurites on the way to their subcapsular
terminations, the fibers given off to the cell-bodies being the terminal portions of such neurites. The latter, as has been said,
end in knob-like swellings which are in contact with the ganglion
cells. Such simple end organs may, in the human sphenopalatine
ganglion, put the preganglionic neurites in communication with
the postganglionic neurones. However, the foregoing results
with methylene blue staining in the sheep raise the question if
these knobs are not, in reality, the first varicosities of an intracapsular end net, the remainder of which has not been differentiated
by the Bielschowsky technique.
SUMMARY
The sphenopalatine, otic and submaxillary ganglia of the sheep
contain multipolar cells with long, slender, frequently branched
dendrites, which extend for considerable distances beyond the
limits of the cell capsules. They resemble in these particulars the
ordinary type of mammalian sympathetic cells.
In the ciliary ganglion the only cells in which processes were
clearly differentiated by methylene blue possessed each a single,
heavy, branched dendrite.
In all the cranial autonomic ganglia (ciliary, sphenopalatine,
otic, submaxillary) the preganglionic neurites terminate on the
cell-bodies of the postganglionic neurones in subcapsular, pericellular end nets of fine varicose fibrils. These endings arc similar
to those of preganglionic fibers in the vertebral and prevertebral
ganglia of the sympathetic system.
CRANIAL AUTONOMIC GANGLIA OF SHEEP 455
BIBLIOGRAPHY
Carpenter, F. W. 1911 The ciliary ganglion of birds. Folia Neuro-biologica,
Bd. 5, pp. 738-754.
HuBER, G. C. 1896 Observations on the innervation of the sublingual and submaxillary glands. Jour. Exper. Med., vol. 1, pp. 281-295.
1899 A contribution on the minute anatomy of the sympathetic ganglia
of the different classes of vertebrates. Jour. Morph., vol. 16, pp. 27-90.
V. KoLLiKER, A. 1894 Ueber die feinere Anatomie und die physiologische Bedeutung des sympathischen Nervensystems. Verhandl. Gesell. Deutsch.
Naturf. u. Aerz., Versam. 66, Theil 1, pp. 97-120.
V. Lenhossek, M. 1894 Ueber das Ganglion sphenopalatinum und den Bau
der sympathischen Ganglien. Beitriige zur Histologie des Nervensystems und der Sinnesorgane. Weisbaden.
• 1910 Ueber das Ganglion ciliare (Vorlaufige Mitteilung). Verhandl.
anat. Gesell., Versam. 24. (Anat. Anz., Bd. 37, pp. 137-143.)
1911 Das Ganglion ciliare der Vogel. Arch. f. mikros. Anat. u.
Entwick., Bd. 76, pp. 745-769.
1911a Das Ciliarganglion der Reptilien. Anat. Anz., Bd. 40, pp.
74-80.
Marinesco, G., Parhon bt Goldstein 1908 Surla nature du ganglion ciliare.
Compt. rend. soc. biol., Paris, tome 64, pp. 88-89.
Michel, J. 1894 Ueber die feinere Anatomie des Ganglion ciliare. Trans. 8th
Internat. Ophthal. Congr. in Edinburgh, pp. 195-197.
MtJLLER, L. R., UND Dahl, W. 1910 Die Beteiligung des sympathischen Nervensystems an der Kopfinnervation. Deutsch. Arch. f. klin. Med., Bd.
99, pp. 48-107.
Retzius, G. 1880 Untersuchungen ueber die Nervenzellen der cerebrospinalen
Ganglien und der iibrigen peripherischen Kopfganglien mit besonderer
Rlicksicht auf die Zellenauslaufer. Arch. f. Anat. u. Physiol., anat.
Abt., pp. 369-402.
Sala, G. 1910 Sulla fina struttura del ganglio ciliare. Mem. istit. Lombardo
scien. e let., classe scien. matem. e natur., vol. 21, pp. 133-139.
Schwalbb, G. 1879 Ueber die morphologische Bedeutung des Ganglion ciliare.
Sitzungsb. Jena. Gesell. f. Med. u. Naturwiss. f. 1878, pp. xc-xciii.
1879a Das Ganglion oculomotorii. Ein Beitrag zur vergleiohenden
Anatomie der Kopfnerven. Jena. Zeitschr. f. Naturwiss., Bd. 13,
pp. 173-268.
PLATE 1
EXPLANATION OF FIGURES
The drawings are camera lucida tracings of ganglion cells stained with methylene
blue, and seen under a 2 mm. oil immersion objective. The dotted lines indicate
the positions of the cell capsules.
1 Cell from the submaxillary ganglion. A, neurite (?).
2 Cell from the otic ganglion.
3 Cell from the sphenopalatine ganglion.
4 Cell from the ciliary ganglion.
456
CRANIAL AUTONOMIC GANGLIA OF SHEEP
F. W. CARPENTER
PLATE 1
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THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 5
PLATE 2
EXPLANATION OF FIGURES
The drawings show the terminations of preganglionic fibers on the cell-bodies of
postganglionic neurones. All are from methylene blue preparations seen under a
2 mm. oil immersion objective. Tlie figures have been drawn to the same scale
with the aid of the camera lucida, which has been used as far as practicable in
reproducing the details of the end nets. Onlj' the fibrils covering the upper surfaces of the cell-bodies have been represented.
5 and 6 End nets from the ciliary ganglion. .1, terminal varicosities.
7 End net from the sphenopalatine ganglion, incomi)letely stained. The out
line of the cell capsule is shown with two nuclei.
8 and 9 End nets from the otic ganglion.
10 End net from the submaxillary ganglion.
458
CRANIAL AUTOXOMIC GANGLIA OF SHEEP
V. W. CAUPENTEU
PLATE 2
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THE CEREBRAL GANGLIA OF THE EMBRYO OF RANA
PIPIENS
F. L. LAND ACRE and MARIE F. McLELLAN
From the Zoological Laboratory of the Ohio State University
ELEVEN FIGURES
CONTENTS
Introduction 461
?slaterial 462
The trigemino-facial complex ' 462
The glossopharyngeal ganglion 464
Tlie lateralis IX ganglion 466
The vagus ganglia 467
The dorsal lateralis X 468
The ventral lateralis X 470
The general somatic X (jugular) 472
The second visceralis X 473
Branchialis X, or first visceralis X 475
Summary and discussion 477
Literature cited 481
[NTRODUCTION
A description of the cerebral ganglia of the frog embryo is
undertaken as a preliminary to the study of the mode of origin of
these ganglia.
This might seem superfluous in view of Strong's ('95) excellent
work on the same subject but Strong's work was pioneer in nature
and since it was published there have appeared a number of excellent papers on the cerebral nerves and ganglia in Amphibia,
particularly those of Coghill ('02) and Norris ('08) in addition
to numerous papers on other Ichthyopsida. While most of these
papers confirm in general the analysis established by Strong,
particularly for the composition of the trigemino-facial complex,
there are certain features in the composition of the glossopharyngo
461
462 LANDACRE AND McLELLAN
vagal complex of ganglia that are not as clear as could be desired
in Strong's work and do not show the resemblance to the type
of composition of ganglia usually found in the Ichthyopsida.
Since the V and VII complex conforms so closely to the type
for Ichthyopsida, one would naturally expect the IX and X complex to be equally true to type, because the V and VII is iisually
the more highly developed and almost invariably has its ganglionic
components more closely fused than IX + X in any given stage.
An examination of embryos younger than that plotted by Strong
shows the IX + X ganglionic complex to be really much more
typical and not so highly fused as shown on Strong's plot, thus
enabling one to make a much more detailed analysis.
MATERIAL
The series of embryos from which two were selected for plotting
consists of eighty-six stages taken from one lot of eggs of Rana
pipiens. The first fifty-three stages were taken at intervals of
two hours beginning six hours after laying. From the fiftythird stage up to the eighty-fifth the intervals were less regular,
ranging from one and three-quarter hours to nine hours, the
average being less than five hours.
Out of this series number seventy-two, 8 mm. in length (171^
hours old) and number eighty-six were chosen for plotting. Number eighty-six is 135 hours older than number seventy-two, being
306^ hours old and 10 mm. in length. In addition to this series,
a 25 mm. tadpole of Rana pipiens was studied and also a 35 mm.
series kindly loaned by Professor Herrick. Neither of these last
two were plotted, but they were carefully compared with the 8
mm. and 10 mm. embryos plotted. Stage 35 mm. seems to be
similar in all essential respects to Strong's plot.
THE TRIGEMINO-FACIAL COMPLEX
In the trigemino-facial complex (fig. 1) one point only needs
to be emphasized, namely, the distinctness of the profundus ganglion. This ganglion, which in earlier stages is much more isolated
than in the 8 mm. embryo, though not entirely distinct, occupies
GANGLIA OF EANA 463
the' dorsal and mesial portion of the ganglion. It extends ventrally as a distinct ganglionic mass about two-thirds of the total
dorso-ventral diameter of the combined Gasserian and profundus.
The ramus ophthalmicus (0. V., fig. 1) seems at this time to come
entirely from the profundus portion, though doubtless there are
fibers in this ramus derived from the ventral portion or Gasserian
ganglion also. This nerve evidently contains later, if not at this
time, the representatives of both the ophthalmic V and of the
opththalmicus profundus of the ganoids. The distinctness of this
ganglion confirms the position taken by Wilder (92, p. 172) and
confirmed by Strong ('95, p. 173), that the ophthalmicus profundus nerve has fused with the ramus ophthalmicus V and that
probably in higher types the profundus ganglion is fused with
the Gasserian.
The infra-orbital trunk arises from the ventral border of the
Gasserian ganglion and immediately splits into the r. maxillaris
and the r. mandibularis. Smaller twigs described by Strong
could not be positively identified. The apparent difference
between the point of origin of nerves in this complex in the 8 mm.
tadpole as compared with Strong's description, is due to the fact
that in the older tadpole the head becomes flat, thus altering the
position of the origin of nerves.
Aside from the difference noted below, the ganglia and nerves
of the 8 mm. tadpole conform closely to the description of Strong,
whose findings we confirm in every detail except that some of
the more minute branches could not be located in our material.
It should be noted here that Strong's nomenclature is followed
throughout in this paper.
The most striking feature in the arrangement of the V + VII
complex is the dorso-ventral elongation as compared with similar
stages in Ameiurus (Landacre '10) and Lepidosteus (Landacre
'12). This is probably due to the fact that it is crowded between
the eye and the ear so that the long axis of this ganglion as well
as of IX + X lies at right angles to the long axis of the body.
It will be noticed in figure 1 that the special visceral or gustatory
portion of the geniculate ganglion could not be identified. This
is in marked contrast to Lepidosteus at a similar stage of growth.
464 LANDACRE AND McLELLAN
THE GLOSSOPHARYNGEAL GANGLION
The visceral portion of the IX ganghon is quite distinct from
the X (figs. 1, 2, 3 and 7). It Hes ventral to the ear capsule,
its anterior end reaching almost to the anterior border of the ear
capsule. The ganglionic cells disappear posteriorly at the level
of the middle of the capsule and the ganglion here dwindles into
a fibrous root which arches around under and behind the capsule
and at the level of its posterior end ascends to enter the medulla
at the same level as that at which the roots of the X enter it. It
was not possible in either the 8 mm. or the 10 mm. stages to identify a special visceral, or gustatory portion, in the visceral IX,
although a more careful study of earlier stages leading up to these
might enable one to identify it.
The anterior end of the ganglion at this stage abuts against
the posterior end of the thymus gland which consists of a dense
mass of lymphocytes, oval in shape and lying at the same level
dorso-ventrally as the glossopharyngeal ganglion. In stages earlier than that figured (figs. 3, 7, T.G.) the ganghon overlaps the
gland to a greater extent, usually lying on the dorsal surface of its
posterior end. These relations are important because of the fact
that in early stages it is difficult to distinguish between the gland
and the ganglion histologically, and further, on account of the
fact that the ramus lingualis of the IX lies on the outer (lateral)
surface and the pharyngeal ramus lies on the inner (mesial) side
of the gland.
At the level of the middle of the ear capsule and at the posterior
border, situated sometimes on the dorsal portion of the root of
the IX sometimes surrounding the root, is a small lateralis ganglion which we have designated the lateralis IX ganglion. This
ganglion, so far as we know, has not hitherto been identified as a
distinct lateralis ganglion in the frog. Strong, however ('95, p.
144), correctly homologizes the nerve arising from this ganglion
(the supra-temporalis) with a lateral line nerve of the IX in fishes.
This is undoubtedly correct, since the ganglion has a separate
existence from early stages and is only accidentally and quite
variously related to the lateral line ganglia of the X.
GANGLIA OF RANA 465
The exact relation of the various ganglia in the IX and X as
figured in plots 1 and 2 to the ganglia shown in Strong's plot
is not always easy to determine.
There can be little doubt, however, that the glossopharyngeal
ganglion is identical with ganglion C of Strong's plot which occupies the extreme anterior end of the IX and X complex. It is
hard to conceive of the IX ganglion of our plot being combined
with X so as not to bring the IX into the position occupied by
ganglion C.
The appearance of the IX ganglion in plots 1 and 2 is strikingly
similar to that of Menidia (Herrick '99) , and of Ameiurus (Landacre '10) and Lepidosteus (Landacre '12) of approximately the
same stage.
In the 8 mm. stage there is only one nerve arising from the
visceralis IX. This is the ramus lingualis of Strong and runs
forward on the outer surface of the thymus gland. In the 10
mm. stage (fig. 2) there are two rami arising from the anterior
end of the ganglion, the larger one running down and forward on
the outer surface of the thymus gland, the ramus lingualis, and a
smaller, the ramus pharyngeus, which runs down and forward on
the inner surface of the thymus gland. We have been able to
detect no trace of the ramus communicans IX ad VII at this
stage in either the 8 mm. or 10 mm. embryo.
In the 35 mm. larva there are three nerves arising from the
anterior end of the IX ganglion. Two of them, corresponding
to the ramus pharyngeus and the r. lingualis of Strong's plot,
undoubtedly arise from the cells of the ganglion, since the fibrous
bundles disappear in the ganglion. Thq third nerve corresponding
to the communicating nerve from IX to VII apparently does not
arise from the ganglion but runs back on the dorsal surface of the
ganglion without diminishing in size and passes into the X ganglionic complex. Its behavior in passing the visceral IX ganglion
furnishes strong evidence that it is probably not visceral hut
purely cutaneous as Strong describes it.
Of the two visceral nerves, the ramus lingualis is much the
larger. It arises from the anterior end of the ganglion and pursues a course downward and forward on the outer surface of the
THE JOURNAL OF COMP.^RATIVE NEUROLOGY, VOL. 22, NO. 5
466 LANDACRE AND McLELLAN
thymus gland. The ramus pharyngeus pursues a similar course
downward and forward on the mesial surface of the thymus gland
and is distributed to the roof of the pharynx. The ramus communicans IX ad VII leaves the dorsal surface of the IX ganglion
at its anterior end and pursues a course forward and downward
on the mesial surface of the thymus gland which it leaves finally
and, swinging towards the middle line of the body, joins the hyomandibular VII at the posterior border of the eye capsule.
The root of visceral IX can be followed with ease on both the
8 mm. and 10 mm. larvae back to the point where it becomes
fused with that of visceral X (figs. 1 and 2, R.IX). At this point
there is not sufficient difference between the fibers of various roots
to enable us to follow them through the ganglion with absolute
certainty. The apparent course is indicated in figures 1 and 2
and at the point of emergence from the X ganglion to enter the
brain the arrangement with one exception agrees identically with
the description of Strong. Strong describes five roots entering
the brain from the X, but up to the 10 mm. stage only four can
be found. The fifth of Strong's nomenclature is a pure motor
root and is probably in our plot combined with the fourth.
THE LATERALIS IX GANGLION
This is a small ganglion situated on the root of the IX nerve
just posterior to and at the level of the middle of the ear capsule
(figs. 1, 2, 5 and 9, L.IX). The position is somewhat variable.
In its early stages it has no connection with the lateralis X ganglion. It does, however, in the later stages become fused more or
less with either the dorsal lateralis or the ventral lateralis. Its
relation with the root of IX is constant, always being in contact
with it. It may lie dorsal, ventral, or posterior to this root, but
its one constant relation is with the IX. The fact that in its earlier
stages it is completely detached from X leaves little doubt that,
while it later becomes fused with X, it is really a lateralis IX ganglion and does not belong morphologically to X. The enormous
size of the auditory capsule, resulting in crowding the root of the
IX back till it joins the X, and the large size of the lateralis X
ganglion account for its later fusion with these ganglia. This
GANGLIA OF RANA 467
ganglion is heavily pigmented like the lateralis ganglion on VII
and X. As to its relation to the lateralis ganglion of Strong's
plot, we are uncertain. As we shall show later, Strong has
apparently overlooked one of the lateralis ganglia on X owing
probably to the extent of the fusion of the IX + X complex.
Since the lateralis IX may sometimes combine with the dorsal
lateralis X, which is probably ganglion A of Strong's plot, and
sometimes with the dorsal border of ventral lateralis X, which
seems to be absent as a distinct ganglion in Strong's plot, it probably corresponds to the ventral border of Strong's ganglion A.
This ganglion is composed, however, as Strong states, of two distinct ganglionic masses, a general cutaneous, the 'jugular,' and
a lateralis X. If it unites permanently with ganglion A, it is
with the dorsal lateralis X.
There is one nerve arising from this ganglion. It is quite
small and pursues in a general way the same course as the auricularis X, being quite separate from it, however, throughout its
whole course. It arises from the ventral and anterior end of the
ganglion and runs forward around the border of the posterior
end of the auditory capsule to reach the epidermis. It is applied
very closely to the capsule and is, of course, displaced backwards
by the later growth of the auditory capsule. This nerve corresponds to the ramus supratemporalis of Strong's plot. The root
of this nerve is difficult to follow but seems to enter the brain along
with the lateralis roots of X. From the ganglion it follows a
course dorsally and posteriorly along the dorsal surface of dorsal
lateralis X, where it seems to join the fibers of this ganglion (figs.
1 and 2).
THE VAGUS GANGLIA
The vagal ganglionic complex consists of five more or less
distinct ganglionic masses (figs. 1 and 2) . With these is associated
in position, as indicated in the preceding section, the lateralis IX
ganglion. These five ganglia fall into three well defined groups.
First, the most dorsal and proximal portion consists of two ganglia;
the dorsal lateralis (D.L.X.) and the jugular or general somatic
(Cu.X.). Of these two, the dorsal lateralis is lateral in position
and the jugular is mesial in position. They are of nearly equal
468 LANDACRE AND McLELLAN
length dorso-ventrally, but the jugular extends farthest forward
and the dorsal lateralis farthest posteriorly.
The second group (figs. 1 and 2) consists of two ganglia, the
ventral lateralis (V.L.X.) and the second division of visceral X
(G.V.X-). This second group lies directly ventral to the first
group. In this second group the ventral lateralis is lateral and
the visceral ganglion is mesial. These two ganglia are approximately equal in their dorso-ventral length but antero-posteriorly
the visceral is broader.
The third group (figs. 1 and 2, G.V.X^) consists apparently of
two branchial ganglia fused, since two branchial nerves arise
from it, but is treated here as one ganglion. It occupies the same
level dorso-ventrally as the second group, but in general shape is
much like the IX ganglion. Its long axis, unlike the two preceding
groups, is in the anterior posterior plane and at its posterior end
it is fused with the second division of visceral X.
THE DORSAL LATERALIS X
This ganglion (figs. 1, 2, 6, 10 and 11), as mentioned above,
occupies the lateral portion of the proximal division of X. It is
also the most dorsal portion of the ganglionic complex. It is
somewhat elongated dorso-ventrally, not reaching so far forward
as the jugular, but extending considerably posterior to any other
portion of the X. It begins abruptly in a rounded anterior end
and diminishes in size as one reads posteriorly, where the most
dorsal of the rami laterales take their origin at the extreme posterior end of the ganglion. The ventral border of this ganglion
is in contact in the later stages, but not in the earlier stages, with
the dorsal portion of the ventral lateralis X. The resemblance
of this ganglion to the lateralis X ganglion in Ameiurus and Lepidosteus (Landacre '10 and '12) at similar stages of growth is
striking. The large size of its cells, its position, its clean-cut
boundaries and the extension of its posterior border beyond the
posterior limits of the remaining ganglia mark it at once as the
same ganglion. Its position with ]-eference to the jugular and
visceral X is the same in all three embryos.
GANGLIA OF RANA 469
The relation of this ganglion to the lateralis ganglion of Strong's
plot is doubtful. Strong figures and describes apparently only
one lateralis ganglion in the X and locates it in ganglion A.
If the dorsal lateralis of our plot corresponds to Strong's ganglion
A, there seems to be no homologue of our ventral lateralis in
Strong's plot. Our ventral lateralis ganglion is quite distinct in
both 8 mm. and 10 mm. embryos but in later stages seems to
become more closely fused with the dorsal lateralis X. It is
very difficult to determine the limits between the two ganglia in
a 35 mm. tadpole. In the 35 mm. tadpole, where the general
arrangement of the ganglia and nerves is quite similar to their
arrangement in Strong's plot, the dorsal lateralis X is still the most
dorsal and posterior portion of the complex.
Dorsal lateralis X in both 8 mm. and 10 mm. embryos gives
rise to one nerve. This nerve arises from the extreme posterior
end of the ganglion and pursues a course directly backwards as
in Lepidosteus, Menidia and Ameiurus. This nerve corresponds
to the most posterior R. lateralis, (1) of Strong's plot, which curves
round behind the auditory capsule before leaving the ganglion.
It splits into two divisions as Strong indicates. Its mode of origin and the general position of the ganglion leave no doubt that
it corresponds to the ramus lateralis of Ameiurus and Lepidosteus.
It also corresponds to the ramus lateralis superior and its dorsal
branch in Amblystoma (Coghill '02), and to the lateraHs mediahs
et dorsalis of Amphiuma (Norris '08).
The root of this ganglion (figs. 1 and 2), which enters along with
the root of the ventral lateralis ganglion and of lateralis IX,
is the most anterior of the roots of X as figured in Strong's plot.
The sympathetic ganglia are discussed here briefly on account
of the proximity of the ganglion sympatheticus cervicale of
Strong's plot (Strong '95, plate 12, gang, sym.) to the proximal
part of the X complex. According to Gaupp ('96), there is no
sympathetic ganglion in the adult frog occupying a position so
close to the X as indicated in Strong's plot.
The adult frog has a sympathetic ganglion on the second spinal
nerve, the sensory part of the first spinal nerve of the 10 mm.
embryo being absent in the adult. From this first sympathetic
470 LANDACRE AND McLELLAN
ganglion a sympathetic cord extends forward and enters the X
complex, from which a second sympathetic nerve runs forward to
unite with the trigemino-facial complex. The connection between
the glossopharyngo- vagal ganglion, the so-called jugular of the
adult, and the trigemino-facial is intracranial. In the 10 mm.
embryo there are sympathetic ganglia on both the first and second
spinal nerves in the usual positions. The sympathetic ganglion on
the first spinal nerve is quite small, as is also the sensory ganglion
of this nerve. The sympathetic ganglion on the second spinal
nerve is, on the contrary, quite large. This, as stated above,
is the first sympathetic of the adult. A careful examination of
our whole series of embryos reveals no sympathetic ganglion in
the region of the X. In fact, up to our latest stage and even in a
35 mm. embryo it is not possible to follow the sympathetic nerve
from the second sympathetic into the X as a continuous cord and
we have been unable to follow with certainty the intracranial connection between X -f IX and V + VII ganglia.
These facts indicate that the sympathetic ganglion and cords
are in a very immature condition in a 10 mm. embryo and even in
a 35 mm. embryo are difficult to follow in detail.
In a 10 mm. embryo the first spinal ganglion is situated 22
sections posterior to the posterior end of lateralis X and the
second spinal ganglion is 43 sections posterior to this point, so
that the first sympathetic ganglion of a 10 mm. embryo which
becomes the first ganglion sympatheticus cervicale is back of the
posterior end of lateralis X, a distance equal to the total anterior
posterior length of IX + X. The change from this condition
to that figured by Strong, if he has correctly located this ganglion,
can only be accounted for by the shifting backwards of the IX -|X complex by the enlargement of the auditory vesicle.
THE VENTRAL LATERALIS X
This ganglion (figs. 1, 2, 6, 10, V.L.X.) occupies, as indicated
above, the lateral position in the most distal and ventral division
of the second group of ganglia. It is elongated dorso-ventrally;
at its dorsal border it is in contact, particularly in later stages,
from 10 mm. on, with the ventral end of dorsal lateralis X and
GANGLIA OF RANA 471
sometimes with lateralis IX. The ventral border of the ganglion
diminishes in size and finally gives rise to a lateral line nerve which
passes out with a visceral nerve of the X.
The mesial border of the ganglion is more or less closely fused
with the lateral surface of visceral X but can always be distinguished from it by the larger size of its cells and by the fact that
the cells are always heavily pigmented. The position of this
ganglion in Strong's plot is difficult to determine. Our series is
not complete from 10 mm. to the 35 mm. embryo. The ganglion
seems to shift its position proximally and join the dorsal lateralis
ganglion, although not completely, since there are lateralis cells
distributed along the dorsal surface of the visceral ganglion in the
35 mm. stage. It must be identified for the present, provisionally,
in part, with the ganglion A of Strong and in part with the general
position of his ganglion B^ and B-, to which he does not attribute
lateralis cells.- The ganglion is not distinct in either Amblystoma or Amphiuma, although Norris ('08) shows in Amphiuma
a rather sharp division between the portion of the ganglion from
which his ramus medialis et dorsalis and that from which his
ramus lateralis vqntralis arises. The former probably corresponds to the dorsal lateralis ganglion of our plot and the latter
to the ventral lateralis. One nerve arises from the ganglion. It
springs from the extreme ventral end of the ganglion and corresponds to the ramus lateralis (5) of Strong's plot. It also corresponds to the ramus inferior (Li.) of Amblystoma (Coghill '02)
and to the ramus lateralis ventralis (Lat. V.) of Amphiuma
(Norris '08).
In the embryo frog, as well as in Amblystoma and Amphiuma,
this nerve passes out of the ganglion in conjunction with visceral
fibers. This is not so evident in Strong's plot, although his
Ramus visceralis does come out of the ganglionic complex at the
same point but the two trunks are separated up to the ganglionic
mass. The conditions in our embryos are quite similar to the
plots of Coghill and Norris, where the lateralis and the visceralis
trunks pursue a similar course for some distance; at least one of
the visceral rami is closely associated with the lateralis ventralis.
The root of the ventral lateralis X passes dorsally to enter the
brain with the roots of the dorsal lateralis X (figs. 1 and 2).
472 LANDACRE AND McLELLAN
THE GENERAL SOMATIC X (JUGULAR)
The somatic X ganglion (figs. 1, 2, 6, 10, Cu.X.) occupies the
mesial position in the proximal mass, or first division of the X
ganglion. It is in the 8 mm. and 10 mm. embryos entirely outside the cavity in which the medulla lies. As the head becomes
broader and the whole X complex assumes a position more horizontal, general somatic X comes to lie ventral to the dorsal lateralis X and also shifts its position somewhat more proximal so that
in a 35 mm. embryo its anterior end is intracranial, the remainder
of it lying in the jugular foramen. This shifting of position gives
the ganglion the general position occupied by the jugular ganglion
in some of the fishes, i.e., intracranial. It extends further forwards than the dorsal lateralis X, but does not reach farther than
the middle of that ganglion posteriorly. Its ventral border is
usually in contact with visceral X, while its lateral, and later its
dorsal border, are in contact with the mesial surface of dorsal
lateralis X. The cells of this ganglion are smaller than those of
either lateralis X but not so closely packed as those of visceral
X. The ganglion is quite large, much la-rger than the jugular at
similar stages in Ameiurus or Lepidosteus.
There is little difficulty in locating this ganglion in Strong's
plot. It represents a portion of his ganglion A. It is quite
distinct in all stages of the embryo up to and including the 10
mm. stage. The most conspicuous nerve arising from this ganglion is the ramus auricularis, (2) of Strong's plot. He figures it as
a pure general cutaneous nerve. It seems to be such in the embryo, but arises from the X ganglion in both An]blystoma and
Ampliiuma as a mixed nerve containing both general cutaneous
and lateralis fibers. Its point of origin from the jugular ganglion
is so close to the dorsal lateralis that there may possibly be lateralis fibers in it. Strong's interpretation of it as a pure general
somatic nerve seems to hold however for the embryos we have
studied.
The ramus auricularis arises from the anterior border of the
ganglion at about tlic middle of its dorso-ventral extent and arches
fonvard and outward to curve around the posterior border of the
auditory capsule. A comparison of figures 1 and 2 will show
GANGLIA. OF RANA 473
that the ramus auricularis X takes its origin from the jugular
ganghon farther posterior in a 10 mm. embryo than in the 8 mm.
stage. A careful examination of twenty series lying between the
8 mm. and the 10 mm. stages shows that in all but one of them the
ramus auricularis arises as in the 8 mm. stage In the 10 mm.
stage this nerve arises posterior to the fibrous bundle connecting
the two ventral ganglia of X to the two dorsal ganglia. This
fibrous bundle passes lateral to the jugular ganglion (figs. 6 and
10) and it is probable that it is the active factor in determining
these relations, i.e., it may form anterior or posterior to the point
of exit of the ramus auricularis from the jugular ganglion.
The differences between the fibers of different components is
not sufficiently great to enable one, at this stage, to follow the
general cutaneous fibers into all the nerve trunks figured by
Strong. The size of the ganglion is entirely sufficient to furnish,
in addition to the ramus auricularis, the rather large bundles
running out in two of th^ branchial rami and the ramus communicans IX ad VII. In describing this last ramus attention was
called to the fact that, while it enters the anterior end of the glossopharj'ngeal ganglion, it runs past that ganghon and follows the
root of the IX to enter apparently the jugular. Questions concerning the composition of mixed nerves are not easily settled on
the material of the age used in this paper. Fortunately most
nerves, even when mixed in the adult and in later embryonic
stages, are likely to be pure and arise separately from a distinct
ganghonic mass if the proper stage is studied. This is true of the
ramus auricularis, but is not true of the other rami arising from
the jugular ganglion, so that our findings as far as they go confirm those of Strong with respect to the rami arising from this
ganglion.
THE SECOND V5SCERALIS X
This ganghon (figs. 1, 2, 6, 10, G.V.X-) occupies the mesial
portion of the distal division of the vagus complex. On its dorsal
and proximal border it is in contact with the jugular and on its
lateral, and later on its dorsal surface, it is in contact with the
ventral lateralis. On its anterior border it is in contact with the
474 LANDACRE AND McLELLAN
branchial X (figs. 1 and 2, G.V.X^). Its longest diameter, like
all other members of the vagus complex except the jugular and
branchial, is the dorso- ventral. It projects somewhat further
caudad than the ventral lateralis but not so far as the dorsal
lateralis.
The position of this ganglion in Strong's plot cannot be determined with certainty. The portion of the X complex from which
the visceral rami arise is represented as a mesial projection
attached to the main ganglionic mass at the level of the ganglion
B^. It is labelled ' ramus visceralis 3' but is described by Strong
as containing ganglion cells. There seems no doubt that the
ramus visceralis (3) of Strong's plot represents the apex of our
visceral ganglion, but whether the proximal part of our visceral
ganglion is represented by B^ or B- of Strong's plot is uncertain.
It is probably represented by B^, since the rami branchiales seem,
on his plot, to come from -B-. The comparison on this basis harmonizes the two plots, since in the earlier stages represented in
our plot the branchial nerves come from the branchial ganglion.
The relations in the 10 mm. embryo plot are quite clear and barring the reduction in the number of branchial nerves are quite
typical.
The visceral nerves arising from this ganglion emerge from
its ventral apex. There are two chief divisions at this stage.
The more ventral arises in conjunction with the ramus lateralis
ventralis {L.X.V., figs. 1 and 2) and the other arises somewhat
more proximally and pursues a course directly posterior. This
last branch is undoubtedly the ramus intestinalis (figs. 1 and 2,
V.X.). As to the composition of the first, the branch arising
with the lateral line ramus, there is less certainty. It probably
is not purely sensory, but contains a large motor ramus, (4) of
Strong's plot. But there are certainly visceral fibers in it also,
probably supplying the fourth gill.
GANGLIA OF RANA 475
BRANCHIALIS X, OR FIRST VISCERALIS X
This ganglion (figs. 1, 2, 4, 8, G.V.X^) stands in sharp contrast
to the remaining portion of X both in its shape and in its position
in the body. It resembles both in shape and position the glossopharyngeal ganglion. Its long axis is parallel to the long axis
of the body. It lies under the auditory capsule like the IX and
not behind it like the remainder of the X. Its general shape
is that of an elongated S-shaped column of cells, free at its anterior border but attached at its posterior border to visceralis X^.
This attachment occurs at the middle or upper third of the anterior surface of the visceralis X. The anterior end of this ganglion
lies under the posterior end of the auditory vesicle. From its anterior end, where a branchial nerve arises, it gradually increases
in size until it fuses at its posterior end with the visceral X-.
The position of this ganglion in Strong's plot is represented
apparently by ganglion B-. It is from this ganglion that the
branchial nerves emerge in his plot and Strong's ganglion C is.
undoubtedly the glossopharyngeal. The only question in doubt
is whether branchial X also corresponds to a part of B'. This
seems improbable since B^ is the only ganglion left on Strong's
plot that could represent the visceral X-. The extent to which
the IX + X complex is elongated by the posterior extension of
the auditory capsule makes it difficult to follow the shifting of
the ganglia, since there is a stage between the time when the
ganglia are distinct, as in our plots, and the time when fibrillated paths can be followed, in which it is very difficult to determine ganglionic boundaries and still more difficult to separate
components among fibers.
An interesting question arises here as to the homology of
the branchial ganglia in the frog with the branchial ganglia of
Menidia, Lepidosteus and Ameiurus. In these types there are
four more or less distinct branchial ganglia in the vagal complex.
In Lepidosteus, which at a similar stage of development most
closely resembles the 8 mm. stage of the frog, only one branchial
nerve, that for the second true gill, arises from the first branchial
X ganglion. The remaining three aiise from the ventral border
476 LANDACRE AND McLELLAN
of the general visceral ganglion, each branchial nerve arising from
a ventral prolongation extending downwards towards the appropriate gill. The condition shown by Herrick ('99, text-fig. 5)
gives the exact relation of these branchial ganglia in Lepidosteus
and Ameiurus, with the exception that the branchial ganglia are
a little larger and somewhat more detached than in Ameiurus
and Lepidosteus and the general visceral portion seems to be
smaller. In the frog there are only two large branchial nerves
and they both arise from the same ganglion. This ganglion has
the same appearance and morphological relations as Branchial X^
of Lepidosteus (Landacre '12). The question arises whether the
branchial ganglion of the frog represents the branchial X^ of
Lepidosteus, Ameiurus and Menidia or whether it represents
two or more branchial ganglia of these types fused. The question
can be answered definitely only by careful study of the embryological development of the branchial ganglia and nerves. The
^condition in the ganoid (Landacre '12) indicates that branchial
ganglia other than X^ are incorporated with the general visceial
X, since these ganglia are much smaller than in Menidia and much
less distinct. The behavior of the second branchial nerve arising
from this ganglion, as will be shown later, indicates that the ganglion that we have called visceralis X^ really represents the general
visceral X of Lepidosteus plus one or more branchial ganglia
and that the branchial ganglia of X (figs. 1 and 2, G.V.X^) represents principally branchialis X^ of Lepidosteus.
As mentioned above, there are two branchial nerves (figs. 1 and
2, Br.X^ and Br.X-) arising from branchialis X. These correspond to the rami branchialis (6) and (7) of Strong's plot. The
anterior (6 of Strong's plot) arises from the extreme anterior end
of the ganglion and pursues a course downward and forward to
the gill. The second (7 of Strong's plot) arises toward the posterior end of .the ganglion and runs downward and forward to the
gill. This nerve on entering the ganglion, however, is not lost
entirely among the ganglion cells, as is the first nerve, but pursues a course backward on the under surface of branchial X until
it reaches the anterior border of visceral X. It is, however, in
its course diminished in size and it may be possible that some of
GANGLIA OF RANA 477
its cells of origin lie in the posterior portion of branchial X. It
is hardly probable that all of them lie in branchial X, so that
until the embryological origin is worked out the problem of the
exact morphology of branchial X^ will have to be left as indicated
above, i.e., that a part of the cells from which the second branchial
nerve (6 of Strong's plot) originates lie in the visceral ganglion and
that the visceral ganglion represents the general visceral ganglion
of such types as Menidia, Lepidosteus and Ameiurus, plus the
representative, one or more, of branchial ganglia of these types.
SUMMARY AND DISCUSSION
1. The trigemino-facial complex of the frog in stages earlier
than those studied by Strong corresponds in all essential details
with his analysis except in the greater isolation of the profundus.
This ganglion in earlier stages is much more isolated than in
the earliest plot given in this paper, but even in that it stands out
rather distinctly, indicating its definite character which is lost
by incorporation with the Gasserian. In other respects we confirm Strong's account of the V + VII ganglia in the frog.
2. The glossopharyngo-vagal complex of ganglia, on the contrary, if taken in the 8 mm. and 10 mm. stages, shows a much
greater degree of simplicity and isolation of its various components than indicated by Strong and furthermore it is much more
typical as compared with such types as Menidia, Ameiurus and
Lepidosteus.
3. The lateralis components in the glossopharyngo-vagal
complex are represented by three more or less distinct ganglia.
These are, (a) a lateralis IX situated on the root of the IX behind
and at the level of the middle of the auditory vesicle dorso-ventrally; (b) two lateralis X ganglia situated on the lateral surface
of the cutaneous and general visceral ganglia respectively. Of
these two ganglia, the dorsal lateralis is proximal and the ventral
lateralis distal. The dorsal lateralis lies lateral to the jugular, or
general cutaneous X, and gives rise to one nerve trunk which
immediately after leaving the ganglion splits, giving rise to the
most posterior ramus of Strong's plot (dorsalis and medialis of
478 LANDACRE AND McLELLAN
Coghill and Norris). This ganglion resembles closely in form
and position the lateralis X of Ameiurus and Lepidosteus in similar stages of development. It extends considerably posterior to
SkTiy other ganglion and the nerve arises at the posterior attenuated extremity as in those types.
(c) The ventral lateralis X is the third of these ganglia. It is
ventral to dorsal lateralis X in young embryos, but later, owing
to the flattening of the head, becomes more lateral in position. It
lies lateral to visceralis X^ in young embryos and later assumes
a more dorsal position with reference to visceralis X^ and also
becomes more closely fused with the dorsal lateralis X. It gives
rise to one nerve which emerges from the ventral apex of the ganglion (the most anterior lateral line ramus (5) of Strong's plot
and the ramus lateralis ven trails of Coghill and Norris).
The presence of two lateral line ganglia on X suggests at once
a homology with the condition in VII where there are two lateral
line ganglia also. As to the distinctness of this ganglion up to
and beyond the 10 mm. stage there can be no doubt. Nor is it
doubtful that it is a lateral line ganglion. The size of its cells,
their heavy pigmentation and the isolation of the ganglion settles
both these doubts. As to the homology with ventro-lateral VII,
we are not willing to go farther at present than to gives it a name
signifying its composition and position in the X complex. It
gives rise to the same component as ventro-lateral VII, it occupies
the same relative position, i.e., lateral to a visceral ganglion and in
the distal portion of the complex as does ventro-lateral VII. Its
nerve also runs out in conjunction with a branchial nerve. If it
should prove to have a similar mode of origin to that ganglion
there would seem to be no objection to homologizing them. No
other fish or amphibian studied so far as we know has a distinct
ventral lateralis ganglion. An examination of the reconstructions of Coghill ('02) and of Norris ('08) indicates that probably
the same condition will be found in Urodeles, since the lateral line
cells extend well down ventrally toward the origin of the ramus
lateralis ventralis in both cases.
4. The jugular, or general somatic X, as in other Ichthyopsida
above the Cyclostomes, is the only representative of its type in
GANGLIA OF RANA 479
the IX + X complex. It is situated mesial to the dorso-lateral
X and is consequently proximal of the visceral X. It is very
large in the tadpole, much larger than in the Lepidosteus and
Ameiurus at the same stage of growth and is much farther away
from the medulla. In the 35 mm. tadpole, however, it migrates
towards the medulla and lies partly, though not wholly, in the
jugular foramen.
One nerVe arises pure from this ganglion at this stage, the ramus
auricularis ; others arise also but run out in conjunction with
other components and could not be accurately traced. So far as
they could be followed their distribution agrees with Strong's
description.
5. The visceral ganglia of the glossopharyngo-vagal complex
lie in three well defined masses: (a) the glossopharyngeal; (b)
the first or most anterior visceral, and (c) the second or most
posterior visceral.
(a) The glossopharyngeal ganglion occupies a position ventral
to the auditory capsule with its long axis parallel to that of the
body. The root is long and curves around behind the auditory
capsule to enter the medulla along with those of X. It seems to
be a pure visceral ganglion, although a cutaneous ramus, r. communicans IX ad VII, passes out from the anterior end of the
ganglion. Its fibers, however, can be traced past the ganglion
and apparently enter jugular X, as described by Strong. It was
not possible in the stages studied to recognize the special visceral
or gustatory portion of this ganglion. Two nerves, the ramus
pharyngeus and the ramus laryngeus, arise from the anterior end
of this ganglion.
(b) The first visceral or branchial ganglion of X resembles
in shape and position the glossopharyngeal. It lies under the
posterior end of the auditory capsule with its long axis parallel
to that of the body. Its posterior end is not, like that of IX,
continued into a fibrous root but joins the cell mass of the second
visceral X near its middle region. Gustatory cells could not be
recognized in this ganglion in the stages studied. Two large
nerves arise from this ganglion, the branchial 6 and 7 of Strong's
plot.
480 LANDACRE AND McLELLAN
The presence of two branchial nerves arising from this ganghon
would suggest that it represented two branchial ganglia fused.
However, there is some doubt as to whether the fibers of the
second branchial nerve arise in this ganglion or partly in this
ganglion and partly in the second visceral ganglion.
(c) The second visceral X ganghon, unlike the glossopharyngeal and the first visceral X, lies with its long axis at right angles
to that of the body. It gives rise to two chief nerve trunks ; one,
the ramus intestinalis and a smaller ramus which probably contains branchial fibers. The question as to the exact position of
the branchial ganglia in these two visceral ganglia cannot be
definitely settled without further examination of earlier stages.
A careful study of a close series of embryos will probably show
definitely the number and position of the epibranchial placodes
and their position in the visceral gangha, thus determining the
number of branchial gangha in this complex and their location.
6. The failure to distinguish special visceral or gustatory
ganglia in Rana in the stages studied is not to be interpreted to
mean, of course, that they are absent or cannot be isolated. As
mentioned in the introduction, this paper is preliminary to a
study of the mode of origin of the cerebral ganglia in the frog. As
a matter of fact, epibranchial placodes are present in the stages
earher than 8 mm. and well defined and seem to behave much as
they do in Ameiurus and Lepidosteus. It is hardly probable
that they will be so distinct or can be followed to so late a stage
as in Lepidosteus, since they are not recognizable in the 8 mm.
stage. Neither is it likely that the frog will furnish such definite
evidence as to the character of placodal ganglia as did Ameiurus,
since all nerves arising from the IX seem to contain both general
visceral and special visceral fibers, whereas in Ameiurus they seem
to contain only special visceral fibers.
7. The results of the present paper emphasize the immense
importance of having access to a large number of stages taken at
close intervals from the same lot of eggs, if one is to reach safe
conclusions in regard to the composition and origin of cerebral
gangha. All ganglia, particularly those derived from the neural
crest, in their early stages are more or less ill defined; following
GANGLIA OF RANA 481
this stage in Lepidosteus, Ameiurus and the frog there is a stage
when the gangha are better defined, have clean cut boundaries
and give rise to fibrillated nerves, usually well isolated from each
other; following this stage the ganglia fuse together more or less,
their nerve trunks combine and they must be isolated largely by
the difference in size of their nerve fibers. Evidently the second
stage is the one most favorable for determining the number and
position of ganglionic components and this stage can be found
only when the series is complete and taken at close intervals.
LITERATURE CITED
CoGHiLL, G. E. 1902 The cranial nerves of Amblystoma tigrinum. Jour. Comp.
Neur., vol. 12, no. 3.
Gacpp, E. 1896 In A. Ecker's and R. Wiederscheim's Anatomic des Frosches.
Braunschweig.
Herrick, C. J. 1894 The cranial nerves of Amblystoma. Jour. Comp. Neur.,
vol. 4.
1899 The cranial and first spinal nerves of Menidia. Jour. Comp.
Neur., vol. 9, no. 3.
Landacre, F. L. 1910 The origin of the cranial ganglia in Ameiurus. Jour.
Comp. Neur., vol. 20.
1912 The epibranchial placodes of Lepidosteus osseus and their relation to the cerebral ganglion. Jour. Comp. Neur., vol. 22, no. 1.
NoRRis, H. W. 1908 The cranial nerves of Amphiuma means. Jour. Comp.
Neur., vol. 15, no. 6.
Stroxg, Oliver S. 1895 The cranial nerves of Amphibia. Jour. Morph., vol.
10, no. 1.
Wilder, H. H. 1892 Die Nasengend von Menopoma alleghanense und Amphiuma tridactylum nebst Bemerkungen iiber die Morphologic des R.
ophthalmicus profundus trigemini. Zool. Jahr,, Abth. f, Anat, n.
Ontog,, Bd, 5, Heft, 2.
THE JOURNAL OF COMPARATIVE XEUROLOGY, VOL. 22, NO. 5
482 LANDACRE AND McLELLAN
ABBREVIATIONS
Aud. v., Auditory vesicle
Aud., Auditory ganglion
Au. X., Ramus auricularis X.
Br. X^, First ramus branchialis X.
Br. X-, Second ramus branchialis X.
Bu. VII., Ramus buccalis VII.
B. v., Blood vessel
Cu. X., Cutaneous or general somatic (jugular) ganglion of X.
D. L. X., Dorsal lateralis ganglion of X.
D. L. VII., Dorso-lateral lateralis ganglion of VII.
Gass., Gasserian or general somatic ganglion of V.
Gen., Geniculate or visceral ganglion of VII.
G. V. IX., Visceral (Glossopharyngeal) ganglion of IX.
G. V. X^, First division of the visceral ganglia of X; possibly equivalent to two
branchial ganglia
G. V. X^, Second division of the visceral ganglia of X.
Hyo. VII., Hyomandibularis VII.
L. IX., Lateralis ganglion of IX.
L. X. v., Ventral ramus of the lateral line nerve of X = R. lateralis (5) of
Strong's plot. Strong '95, plate 12
L. X. D., Dorsal ramus of tKe lateral line nerve of X = R. lateralis (1) of
Strong's plot. Strong '95, plate 12
Man. v., Ramus mandibularis V.
Max. v., Ramus maxillarus V.
Mes., Mesencephalon
No., Xotochord
0. v.. Ramus ophthalmicus V.
0. S. VII., Ramus ophthalmicus superficialis VII. .
Opt., Optic vesicle
P(d. VII., Ramus palantinus VII.
Prof., Profundus ganglion
R. F., Root of V.
R. L. IX., Lateral line root of IX.
R. IX., Root of IX.
R. P. IX., Ramus pharyngeus IX.
R. X. V + C, Visceral + somatic roots of X.
72. L. X., Lateral line root of A' + IX.
R.X.,RootoiX.
S. T. X., Ramus supra-temporalis X.
T. G., Thymus gland
V. L. VII., Ventral latcriil line ganglion of VIL
V. L. X., Ventral lateral line ganglion of X.
V. X., Ramus visceralis X.
GANGLIA OF RANA
483
Man.V,
R L.IX
'.HyoVII
Fig. 1 A fiat reconstruction of the V, VII, VIII, IX and X cerebral ganglia in
Rana pipiens, 8 mm. in length. The scale at the top of the figures indicates the
position and number of sections 10// in thickness over which the plot extends.
General somatic ganglia are shown with horizontal lines, lateral line ganglia with
cross hatched lines, and visceral ganglia with vertical lines. Special visceral or
gustatory ganglia are not indicated, as their boundaries could not be determined
in embryos of this age. X 100.
484
LANDACRE AND McLELLAN
fc w -ro 3S io is JO /s
LXV. '^^ X
6&C 3936 3/ -26
Fig. 2 A flat reconstruction of the IX and X cerebral ganglia of Rana pipiens
10 mm. in length ; shading as in figure 1 . The scale at the top of the figure indicates
number and position of sections lO^t in thickness over which the plot extends. The
scale at the bottom of the plate indicates the number of the section and the number of the figure illustrated in succeeding plates. As in figure 1, the special visceral or gustatory ganglia are not indicated. 1, 2, 3, 4 are the first four roots
according to Strong's nomenclature (Strong '95, plate 12, fig. (a) and page 135).
X 100.
Fig. 3 A camera outline through the dorsal portion of the riglit side of the head
of Rana pipierKS, 10 mm. in length. The section passes through the anterior end
of the IX ganglion and the origin of the ramus laryngeus. The position of the section on figure 2 is indicated at the bottom of that figure (Sec. 2). The details of
the area blocked out are shown on figure 7. X 50.
GANGLIA OF RANA
485
Fig. 4 A camera outline through the dorsal portion of the right side of the head
of Rana pipiens, 10 mm. in length. The section passes through the middle of the
first portion of the visceral X ganglion {G.V.X^, fig. 2) and the posterior portion of
first branchial nerve {Br. X^) of that ganglion. The position of the section is indicated at the bottom of figure 2 (Sec. 26). The details of area blocked out are shown
in figure 8. X 50.
Fig. 5 A camera outline of the dorsal portion of the right side of the head of
Rana pipiens, 10 mm. in length. The section passes through the lateralis IX
(L.IX.) and the second visceral ganglion of X ((?. V. X^). The position of this
section is indicated at bottom of figure 2 (Sec. 31) and the details of the area
blocked out are shown in figure 9. X 50.
Fig. 6 A camera outline through the dorsal portion of the right side of the head
of Rana pipiens, 10 mm. in length. The section passes through the four posterior
masses of the X ganglion. The position of this in figure 2 is indicated at the bottom of that figure (Sec. 36). The details of the area blocked out are given in figure
10. X 50.
486
LANDACRE AND McLELLAN
B.V.,
--:» 6e©-0©©e,o<5*'e, Aud.V.
v« t
^v. X
Fig.
Fif^.
l-'ig.
Fig.
Fig.
figiin;
7 Details of area blocked out in figure 3. X 200.
8 Details of area blocked out in figure 4. X 200.
Details of area blocked out in figure 5. X 200.
10 Details of area blocked out in fisun; (i. X 200.
11 Details of the lateralis X ganglion. The position of this section on
2 is shown at the bottom of tlial fiKun; (Sec. 30). X 200.
DEGENERATION AND REGENERATION OF NERVE
FIBERS
S. WALTER RANSON
From the Anatomical Laboratory of the Northwestern University Medical School^
TWENTY-NINE FIGURES
The series of experiments upon which this paper is based
was begun with no idea of taking up the question of the regeneration of nerve fibers, but with the much more restricted purpose of studying the degeneration of the non-medullated fibers
of the spinal nerves. After it had been demonstrated that the
spinal nerves contain many more non-medullated than medullated fibers (Ranson '11) it was very desirable that the Wallerian experiment should be repeated to determine the direction
of degeneration in these fibers. Work had not progressed far,
however, before it became evident that observations were being
made that had a bearing on the perplexing question of nerve
regeneration and made it necessary to enlarge the scope of the
investigation while not abandoning its original object.
Since, as has been intimated, we shall be concerned in part
with the degenerative and regenerative phenomena in the nonmedullated fibers, it will be best to indicate at this point the
facts which have been previously ascertained in regard to these
fibers.
When ordinary staining methods are used it is possible to
see in the spinal nerves only those fibers which possess a myelin
sheath, since axons not so covered cannot be differentiated
from the connective tissue of the endoneurium. But when
^ Some of the work, on which this paper is based, was done in the Anatom.
biol. Institut, Berlin, the Anatom. Anstalt, Freiburg i. Br. and the Phtsiol.
Institut, Freiburg i. Br. To the directors of these institutes I am indebteoFor
many courtesies.
487
THE JOURNAL OF COMPARATIVE NEUROLOCJT, VOL. 22, NO. 6
DECEMBER, 1912
488 S. WALTER RANSON
these nerves are stained by a modification of Cajal's method,
which we have called the pyridine-silver method, very many
fine nerve fibers are seen in the endoneurium between the medullated fibers (Ranson '11). These are stained black with reduced
silver and are devoid of a myelin sheath, while the medullated
axons are light yellow and are surrounded by a colorless sheath
of myelin. The non-medullated fibers may run singly but are
usually grouped into small bundles. Although no attempt
has been made to determine their exact number, it is easy to
see that they far outnumber those which are medullated. On
tracing these fibers back toward the spinal cord, it is found that,
while a certain number can be seen entering the nerve via the
gray ramus communicans (Chase, unpublished observations),
the vast majority of them enter the nerve by way of the dorsal
root. A study of the spinal ganglion (Ranson '12) has shown
that these fibers are derived from the axons of the small cells
of the ganglion by a T- or F-shaped branching. Because of
the location of the cells of origin in the spinal ganglion, and
because of the characteristic T- or F-shaped branching of the
axons there need be no hesitancy in regarding them as afferent
and not sympathetic in function.
As has been intimated, it was our purpose, when the series
of experiments to be reported in this paper was begun, to cut
first the peripheral nerve and then, in other experiments, the
roots proximal to the spinal ganglion in order to determine the
direction of degeneration of these fibers. The division of the
sciatic nerve of the dog was undertaken to exclude by the direction of degeneration the possibility that some of the nonmedullated fibers might arise from cells located at the periphery
(a common location of such cells in invertebrates). In another
series of experiments the roots, proximal to the ganglion of the
second cervical nerve of the dog, were cut to determine whether
any non-medullated fibers arose from cells located in the gray
substance of the spinal cord. Since the results of these two
series of expei'imcnts were complicated by a variety of regenerative changes in the nerve, ganglion and roots, it has seemed best
to present the two series of expei-iments in separate papers.
DEGENERATION AND REGENERATION OF NERVE FIBERS 489
And the present paper will be concerned only with the results
of section of the sciatic nerve.
The majority of those who have worked with the problem
of the regeneration of nerves had previously taken a definite
position in the contest over the neurone theory and sought in
their experiments on nerve regeneration to find evidence which
would aid them in maintaining that position. The supporters
of the neurone theorj- believed that the axons were formed
embryologically as outgrowths from ganglion cells and were
regenerated from the axons of the central stump toward the
periphery. On the other hand, the opponents of the neurone
theory believed in a multiple origin of the axons from the cells
along the course of the embryonic nerves, and described a similar discontinous origin of the new axons in regenerated nerves
by a differentiation of the protoplasm formed from the old
neurilemma cells. The present writer, having never committed
himself in the matter of the neurone theory, was able to take
an entirely unprejudiced attitude and was led to his present
position as he studied the regenerative phenomena which
appeared, unexpectedly and with great clearness, in the preparations of the divided sciatic nerve.
SURVEY OF THE LITERATURE OX THE REGENERATION OF NERVES
Even before the time of Waller the subject had received some
attention, but it was he who first recognized the true nature
of the degenerative and regenerative processes in nerves. He
stated ('52) that that portion of a divided nerve fiber separated
from its trophic center underwent complete degeneration and
that regeneration took place through an outgrowth of new
fibers from the central undegenerated stump. His conclusions
were not at once accepted, however, and even to the present day
the outgrowth of the new axons from those of the central stump
is a matter of debate. It would tax too heavily the reader's
patience to review the literature from Waller's time to the present
date, but this is made unnecessary by the excellent reviews of the
early literature, given in the articles of Howell and Huber ('92)
and Stroebe ('95). According to the summary given by Howell
490 S. WALTER RANSON
and Huber of the problem as it stood at the time of the writing
of their article, three views were then held: (1) According
to one view, the axons did not degenerate in the peripheral
stump after they had been separated from the central nervous
system, so that, after the two ends of a cut nerve had been
approximated, it was only necessary for a peripheral axon to
fuse with a central axon and for a new myelin sheath to be developed about it. (2) The view most generally current at that
time was the view of Waller that the new axons grew out from
the central end. (3) But they state that the best of the papers
which had appeared in the years immediately preceding their
work agreed in stating that the axis cylinder is developed anew
in the peripheral end and is connected secondarily to the central end. They add that those who maintained that the new
axis cylinders are sprouted from the old ones of the central end
did not claim to have seen the process, since the closest study
with the staining method then in use showed nothing of the
axis cylinder at the point of transition. In the opinion of the
present writer, it was just this lack of a satisfactory axon stain
and the resulting uncertainty of what was occurring at the
transition zone between the ends of a cut nerve that has made
it possible for the supporters of the theory of the autogenous
regeneration of nerves to maintain their position for so many
years.
With the work of Blingner ('91), Howell and Huber ('92),
Stroebe ('93) and Huber ('95), the modern work on the regeneration of nerves may be said to have begun. Blingner ('91)
saw and clearly described the formation of the nucleated protoplasmic bands which have occupied so prominent a place in
the supposed histogenesis of autogenously regenerated nerve
fibers. According to him, the nuclei of the neurilemma increase
in number and protoplasm accumulates about them. Longitudinal striation appears in the protoplasm of these cells which
then become fused into long multinucleated bands. Within
these bands the centrally placed, longitudinally striated protoplasm becomes differentiated into a new axon, while in the
surrounding protoplasm the myelin sheath is laid down.
DEGENERATION AND REGENERATION OF NERVE FIBERS 491
Howell and Huber ('92) also saw and described these protoplasmic bands, and, while they were unable to confirm Biingner's
observations on the differentiation of axons in them, they regarded them as 'embryonic nerve fibers' capable of receiving and
conducting impulses. In case of a failure of the two ends of
the nerve to unite, regeneration stopped with the formation of
the protoplasmic bands. In case of union of the two stumps,
the bands of the peripheral stump fused with those of the central stump ; next myelin sheaths were laid down within the bands
and new axons grew down into them from the central stump.
Stroebe ('93), using his now well known stain, was able to
demonstrate the outgrowth of new axons from the central end,
but thought that the myelin sheath was formed as a continuation of the old sheath and accompanied the axon in its forward
growth. He was unable to demonstrate any connection between these new fibers and the protoplasmic bands seen by
Biingner in the peripheral stump.
Working with Stroebe's method, Huber ('95) was able to
secure much clearer pictures of the regenerating nerve fibers
than had been seen before, and showed that the axons grew out
from those of the central stump and, in some cases at least, entered the substance of the protoplasmic bands of the peripheral
stump. He was able to see some which ended abruptly in the
protoplasm of the bands, their free ends directed toward the
periphery and occasionally presenting bulbous enlargements.
Ziegler ('96) ascribed the origin of the new axons to the neurilemma cells of the central stump and thought that at the time
of their first appearance they had no connection with the old
axons. Galeotti and Levi ('95), Kennedy ('97), and Wieting
('98) thought that the new axons developed in situ in the peripheral stump. It is clear, therefore, that even before Bethe began
his work the opinions of those who had worked at the question
from the histological side were about evenly divided. This
shows that the histological methods at their disposal were not
adequate for the solution of the problem.
Since investigators had failed to show conclusively the nature
of the regenerative processes • when the two stumps had been
492 S. WALTER RANSON
allowed to unite, Betlie ('03) decided to follow the example of
Philipeaiix and Vulpian ('59) and determine what would occur
in a nerve fully cut off from its central connections. He worked
with the sciatic nerve of young dogs and to prevent the union
of the cut ends he adopted special operative procedures: (1)
In some dogs he grasped the sciatic nerve at the great sacrosciatic foramen, tore it out along with the motor roots and
spinal ganglia and cut it off in the middle of the thigh. (2) In
others he cut the sciatic in the middle of the thigh, left the
peripheral stump in place, cut off 3 cm. from the central stump
and thrusting it through one muscle, sewed it into another.
At that time he considered the second method as reliable as
the first. In these ways he believed that he had effectually
excluded the possibility of any union between the central and
peripheral stump; and in carefully conducted autopsies he was
unable to find any trace of such connection in those cases which
he considered successful. Also physiological evidence of the
absence of connection between the central and peripheral ends
was obtained at autopsy in the absence of reflex movements
on stimulating the distal stump and the absence of movement
in the muscles innervated by the sciatic nerve on stimulation of
the central stump.
Under these circumstances, which seemed both anatomically
and physiologically to exclude the possibility of any union with
the central nervous system, Bethe obtained evidence of regeneration in the peripheral stump. Many medullated fibers were
present. Stimulation of the peripheral stump caused contraction in the muscles of the leg but no reflex movements. He
also noticed that some time after autogenous regeneration had
occurred a slow degeneration set in which caused, after a time,
the complete disappearance of all regenerated fibers. This
Bethe considers an important point in favor of the autogenous
nature of their regeneration, since, he assumes, fibers which
have formed central coimections do not undergo a second degeneration. In his somewhat limited study of the development
of these autogenously regenerated fibers he distinguishes five
stages: (1) protoplasmic band formation; (2) differentiation
DEGENERATION AND REGENERATION OF NERVE FIBERS 493
of these bands into axial strands and granular sheaths 'Achsialstrangfasern' ; (3) appearance of fibrils in the axial strands in
the neighborhood of the nuclei; (4) fusion of these discontinuously formed fibrils- into fibrillar bands; (5) discontinuous
formation of a myelin sheath, Bethe maintains that such
transformation can occur only in young animals and even then
only in a limited number of the fibers. Many fibers in young
animals and all in adult animals are incapable of developing
beyond the stage of protoplasmic bands without some stimulus
from the central stump.
So convincing did these experiments of Bethe appear that
they excited the greatest interest and have led to many attempts to secure confirmation of his results. Miinzer ('02),
Head and Ham ('03) and Mott, Halliburton and Edmunds
('04) presented evidence to show that all new axons in the peripheral stump were outgrowths from the old axons of the central
end. But there have appeared two investigations, those of
Langley and Anderson ('04) and Lugaro ('05), which not only
show that Bethe's conclusions were wrong, but show clearly
the fallacies upon which his erroneous conclusions were based.
The work of Langley and Anderson ('04) was carried out on
kittens and young rabbits. Experiment 5 is typical of their
results. The right sciatic nerve was cut high up in the thigh,
turned down and sewed into the skin above the knee. After
251 days the sciatic was cut above the first point of section
and the femoral nerve was cut near the inguinal ligament. The
peripheral sciatic stump, twelve days after the second operation,
contained no sound medullated fibers but many degenerated
ones. Summing up all their experiments they say:
We find that all the medullated nerve fibers, which reform in the
peripheral end of a nerve, degenerate when the nerves which run to
the tissues near the cut end are cut near the spinal cord; in other words,
in our experiments all medullated fibers in the peripheral ends of the
cut nerves were fibers which had become connected wth the central
nervous system. If then, autogenetic regeneration of fibers had occurred, every one of them had become connected with the central end
of some nerve fiber. On the autogenetic theory this seems to us in
the highest degree unlikely.
494 S. WALTER RANSON
It is important not to overlook the possibility of fibers growing into the distal stump from other nerves in the neighborhood.
Against the physiological tests of the absence of connection
between the two ends of a divided nerve, failure to get reflex
movement on stimulation of the peripheral stump or movement
in the muscles of the leg on stimulation of the central stump,
tests upon which Bethe has always laid the greatest stress, Langley
and Anderson raise the following objections: (1) In some experiments in which anatomical connections could be demonstrated
they were unable to get any reflex response by stimulating the
peripheral stump. (2) It is possible that at a certain stage of
regeneration the conductivity of the junctional portion is too
small to give a reflex effect under the conditions of the experiment. (3) When the regenerated axons come from the femoral
or obturator, as is sometimes the case, stimulation of the central end of the sciatic would not affect them.
Lugaro ('05) saw that the operative methods employed by
Bethe, did not exclude the possibility of downgrowth of axons
from fibers still connected with the central nervous system.
In order to remove all possible sources of such contamination,
he resected the lumbo-sacral nerves together with their associated spinal ganglia at their exit through the dura mater in
young dogs and cats, and was unable to find any medullated
fibers in the sciatic four months after the operation. In three
young dogs, in which he removed the lumbo-sacral spinal cord
and its associated spinal ganglia he found after three months
the same absence of medullated fibers in the sciatic nerve.
Raimann ('05) cut away that portion of the lumbo-sacral
spinal cord and associated ganglia from which the sciatic nerve
arises; but his positive results, taken in connection with the
negative ones of Lugaro, can only show the great tendency for
fibers to grow into the degenerated sciatic from the obturator
and femoi-al, which with their associated portion of the spinal
cord remained intact in Raimann's experiment.
Segale ('03) is of the same opinion as Lugaro and distinguishes
between compensation due to ingrowth from other nerves and
DEGENERATION AND REGENERATION OF NERVE FIBERS 495
regeneration — processes which are associated in the functional
restoration of divided nerves.
We must still mention briefly a few of the less important
contributions on the side of autogenous regeneration. Van
Gehuchten ('04) repeated Bethe's experiments with positive
results, but did not make a microscopic examination of the
intervening scar nor attempt to cause the degeneration of the
new fibers by secondary section of all the nerves going to the
leg. Ballance and Stewart ('01), Fleming ('02), Durante ('04),
and Modena ('05), have made observation in favor of an autogenous regeneration of nerve fibers; but since they present no
new evidence we need not go into their work in detail here.
Bethe ('07) has attempted to meet the objections raised by
his opponents, but, as it seems to the present writer, with very
little success. So far as his paper is not a mere repetition of
former experiments it may be divided into three parts: (1) He
considers the facts brought to light by Cajal's new silver method,
but we can best take up Bethe's objections to this method in
another part of this paper. (2) He reports experiments to show
that when an axon is divided near its cell of origin no regeneration occurs. That his negative results, so far at least as the
spinal ganglion is concerned, are to be explained on the basis
of inadequate histological methods, will be shown in another
paper when the effects of cutting the nerve roots are taken up.
(3) He presents experiments designed to meet the objections
of Langley and Anderson and Lugaro. In spite of the length
already reached by this review it will be necessary for us to
analyze these experiments in some detail.
In reply to Lugaro he presents a case, in which after extirpation of all the roots belonging to the nerves going to the hind leg,
regeneration was recognizable in the peripheral sciatic stump.
In a young dog he tore out both sciatic nerves, but failed to
bring the spinal ganglia with them in either case. Several
weeks later he opened the canal and removed on the left side the
2 to 7 L. and 1 S. roots. Some months later regeneration could
be demonstrated in the peripheral stump. But there is one
496 S. WALTER RANSON
serious objection to this experiment, since previous to the removal
of the roots and gangha on the left side he had torn out both
sciatic nerves. Hence there was present in the pelvis the torn
central fragments of the right sciatic nerve. So great was the
regenerative energy of this right sciatic stump that it was found
at autopsy that its fibers had grown out of the right great sacrosciatic foramen and established an anatomically demonstrable
connection with the right peripheral stump. Under these circumstances it is hard to convince oneself that a few regenerated
fibers may not have taken a different course, grown across the
anterior surface of the sacrum out of the left great sacro-sciatic
foramen and down to th'e left peripheral stump. Bethe's other
experiments with removal of the roots were negative, a fact
which he can only explain as due to the poor state of the general
health of the dogs upon which so mutilating an operation had
been performed.
To meet the objections of Langley and Anderson he performed
two experiments in which several months after the tearing out of
the sciatic he tried to cut all possible connections with the spinal
cord and six days after the secondary operation still found
undegenerated medullated fibers in the peripheral stump. But
in one of these cases it is clear that all possible central connections were not divided. In this case the second operation consisted in cutting the roots associated with the nerves going to
the leg, and as autopsy showed, he failed to cut the 1 S. root.
In the other experiment the secondary operation consisted in
(1) cutting the femoral and obturator near the pelvis, (2) cutting
the 1, 2, and 3 S. nerves at their exit from the intervertebral
canal, and (3) ligature and division of the tissue at the normal
point of exit of the sciatic nerve. Since in the primary operation the 6th and 7th L. roots and ganglia had been torn out
with the sciatic, this control seems to have been fairly complete. '
It is plain however that this experiment was very complicated
and gave opportunities for error in the operations and subse(luent observations. In the opinion of the present writer the
positive results of Bethe in these three cases are to be attributed
to his habit of tearing out the sciatic nerve, producing a lesion
DEGENERATION AND REGENERATION OF NERVE FIBERS 497
of unknown extent at an unknown level and rendering difficult
the accurate application of Langley and Anderson's test of the
presence of central connections by subsequent division of all
nerves going to the leg. Positive results obtained by complicated and uncertain methods cannot outweigh the negative
results obtained by simpler operative procedures.
More recently Wilson ('09) has repeated some of Bethe's
work but came to no definite conclusions as to the nature of
the processes involved in the regeneration of nerves.
Space has not permitted a detailed report of all the work that
has been done with the object of studying the changes which
occur in a piece of nerve permanently cut off from the central
nervous system; but enough has been given to show that this
line of experimentation has, as yet, given no satisfactory evidence of the capacity of a stretch of nerve completely separated
from the central nervous system to undergo an autogenous regeneration. On the contrary, the more recent experiments of this
sort show that so great is the regenerative capacity of the central stump in young animals that it is a matter of the greatest
difficulty to exclude the possibility of axons from the central
having reached the peripheral stump, and it is equally difficult
to exclude the possibility of axons having grown into the peripheral stump from other nerves in the vicinity. The only experiments that are entirely satisfactory are those of Lugaro, involving the removal of the entire lumbo-sacral portion of the spinal
cord and the associated spinal ganglia, and these experiments
were negative.
The reason that so many have attempted to solve the problem
in this way is that no stain was available prior to 1903 which
was capable of unraveling the complicated processes going on
at the point of union of the cut ends of a divided nerve; and
any attempt to determine what was going on in this zone with
the use of any of the usual stains could scarcely" lead to convincing results. Under these circumstances it was but natural
that an effort should be made to determine what happened
under much simpler conditions in an isolated peripheral stump,
not with the idea that any regeneration occurring here would
498 • S. WALTER RANSON
be essentially different from that occurring when the two ends
are in apposition, but with the idea that the process would be
easier to analyze, and that in this way evidence would be obtained
which could be applied in the analysis of the more complex
conditions obtaining in the divided and reunited nerve.
Fortunately we now have in the method of Cajal a technique
giving a sharp stain of the finest branchings of axons and
enabling the investigator to see clearly the complicated changes
going on near the cut surfaces and to correctly understand the
mechanism of nerve regeneration. With the solution of the
problem, which is given by this new method of staining, there
ceases to be any reason for an attempt to secure an isolated
stump for study, since it would be highly improbable that there
would occur in an isolated stump a process which was essentially
different from that which occurs in the peripheral stump when
in connection with the central nervous system.
A number of observers have made use of Cajal's method for
the study of degenerative and regenerative changes in nerve
fibers. Perroncito ('05) and Cajal ('08) have obtained brilliant
results. Marinesco ('05, '06), Poscharissky ('07) and Tello ('07)
have also made use of this method. As we proceed with the
discussion of our own results we will point out in what ways
our results differ from those of others who have used this method.
TECHNIQUE
The experiments were made on the sciatic nerve of adult
dogs. With strict aseptic precautions the nerve was exposed
in the upper part of the thigh and cut with a sharp scalpel or
scissors. The ends were in some cases allowed to retract; in
others a stretch of 1 cm. was removed and retraction allowed;
and in still others, without resection of any of the nerve, the
two ends were approximated with sterile silk or catgut sutures.
The dogs were allowed to live for a period of from one to thirtyfive days and at the autopsy a short stretch of the proximal
stump and a longer stretch of the distal stump together with
the intervening scar were removed and subjected to histological
analysis. Since we deal only with the early stages of regenera
DEGENERATION AND REGENERATION OF NERVE FIBERS 499
tion, and with them only from the histological standpoint, little
if any information would have been secured by electrical stimulation of the stumps. The omission of these physiological tests
of regeneration was the more excusable, since, as has been mentioned, the majority of the autopsies were complete before it
was determined to extend the scope of the study from the degenerative changes to include the regenerative processes as well.
With two exceptions the wounds healed by primary intention.
In Dog III the cutaneous stitches came out on the fourth day,
but this dog was killed on that same day and the deeper parts
TABLE 1
NUMBER OF
DAVS BETWEEN OPERATION
AMOUNT OF NERVE
WHETHER SUTURED OR
EXPERIMENT
AND AUTOPSY
REMOVED
ALLOWED TO RETRACT
I
1
None
Sutured
II
35
None
. Sutured
III
4
None
Sutured
IV
8
None
Sutured
V
14
None
Sutured
VI
19
None
Sutured
VII
34
1 cm.
Retracted
VIII
34
None
Sutured
IX
25
None
Sutured
X
25
1 cm.
Retracted
XI
1
None
Retracted
XII
2
None
Retracted
XIII
3
None
Retracted
XIV
4
None
Retracted
of the wound were free from infection. Dog ix became infected
and was discarded. Dog i died about twenty-four hours after the
operation probably from late effects of the anaesthetic. The
other dogs remained in excellent health until they were killed.
Table 1 shows what experiments were made.
The tissue was prepared by the pyridine-silver modification
of Cajal's method, the steps of which are as follows: The nerve
is placed for forty-eight hours in absolute alcohol to which has
been added 1 per cent of strong ammonia. The pieces are then
washed for two minutes in distilled water and transferred to
pyridine for twenty-four hours, after which they are washed
in many changes of distilled water for twenty-four hours. They
500 S. WALTER RANSON
are then placed in the dark for three days at 35°C. in a 2 per
cent aqueous solution of silver nitrate, then rinsed in distilled
water and placed for one or two days in a 4 per cent solution of
pyrogallic acid in 5 per cent formalin. Sections are made in
paraffin and after mounting are ready for examination. This
modification has many advantages over the original Cajal method
when applied to the peripheral nervous system. It is only occasionally that one obtains with the older method a satisfactory
stain of the non-medullated fibers, while when pyridine is used
these fibers stand out with great clearness, not only in their
normal state but also in the early stages of degeneration. The
various regenerative phenomena in these fibers also stand out
with great clearness. Cajal was able with his method to observe
some of these changes in the non-medullated fibers but seems to
have seen relatively few of these fibers showing that his method
was not especially suited for their study. Perroncito ('09), who
used the original method, states that 'Hhe first phenomenon
which is noticed in the peripheral stump of a divided nerve is
a clearer differentiation of bundles of non-medullated fibers
which run between the medullated fibers." The old Cajal
method in the hands of the writer has, only rarely, given a clear
differentiation of the non-medullated fibers, and one gathers
from the statements of Perroncito and Cajal that it has only
been in injured nerves that they have seen them clearly, and
even then with less distinctness than that with which they
appear in the pyridine-silver preparations. They consider that
these fibers are of sympathetic origin and fail entirely to appreciate their great number. As a result of the inadequacy of the
old Cajal method many of the most important steps in the degeneration and regeneration of these fibers also escaped their attention. It is evident, however, from their figures and descriptions
that when they use the term 'non-medullated fibers' they refer
to the same structures which are designated by that name in
the present paper.
Another objection to the old (iijal method, as apphed to the
study of regenerating nerves, is that by this method it is difficult to get both the old and the new axons to stain in the same
DEGENERATION AND REGENERATION OF NERVE FIBERS 501
preparation, as each requires a different amount of ammonia
in the fixing solution (Cajal '08). Cajal advises the use of a
mixture of medium strength in order to stain both, but says
that in practice it is very difficult to get just the right concentration. All this difficulty is avoided by the use of pyridine,
which causes the old medullated axons to stain yellow and the
old non-medullated axons, as well as all newly formed fibers, a
dark brown or black. The new technique is also much more
certain in its results. With pure chemicals and clean glassware no failures need be anticipated. It also has the advantage of giving a uniform stain throughout a large piece of tissue.
Against the use of the Cajal method in the study of regenerating nerves, Bethe ('07) has raised the following objections:
(1) The myelin sheaths are not stained. This is of course true
and, since these sheaths are represented only by colorless spaces,
the method is of little or no value in the study of their degeneration and regeneration. If, however, we wish to study the
changes in the axons, this very transparency of the mj^elin
sheaths renders the preparations more serviceable. The verj'
faint yellow of the connective tissue and the transparency of
the myelin sheath make it possible to use relatively thick preparations (12 to 15/i) in which the axons can be followed for
a relatively long distance. (2) It shrinks the axons. This is
also true and is a defect which it has not been possible to overcome. (3) It is uncertain in its action. Bethe excuses himself
for not having used Cajal's method by saying that his material
was too valuable to jeopardize by the use of such an uncertain
technique. This objection certainly cannot be applied to the
pyridine-silver method. (4) Only very small pieces of tissue
2 or 3 mm. thick can be used. On the contrary, either with the
old Cajal method or the pyridine-silver modification, the best
results are obtained with larger pieces. It is, of course, essential
that one be able to study large sections in order to secure a
correct idea of what is going on at different levels. The preparations which form the basis of this paper are, for the most part,
longitudinal serial sections of pieces of nerve from 5 to 8 mm.
thick and from 15 to 20 mm. long. They represent sometimes
502 S. WALTEE RANSON
the central or peripheral stump by itself, sometimes the two
united stumps with the intervening scar. These large pieces
of tissue were none too large, as the staining is perfect throughout. The use of such serial sections makes it possible to trace
with certainty the course of the axons, but has involved the
preparation of several thousand sections,, and has precluded the
use of other stains.
The results of this investigation can best be assembled under
the following headings:
Earl} changes in the distal stump
1. Degeneration of the medullated fibers and formation of nucleated pro
toplasmic bands
2. Degeneration of the non-mcduUated fibers and the formation of nucleated
protoplasmic bands
3. Abortive autogenous regeneration in the distal stump
Early changes in the proximal stump
1. Changes in the non-meduUated fibers
Early abortive regeneration
Cellulipetal degeneration
Formation of new axons
2. Changes in the medullated fibers
Formation of a zone of reaction
Fibrillar dissociation
Early branching of the axons in the immediate neighborhood of the
lesion
Formation of lateral branches at some distance above the lesion
Formation of fiber bundles and skeins
Mechanism of the regeneration of nerve fibers
1. Proliferation of axons in the central stump
2. Penetration of the new axons through the scar
3. Utilization of the protoplasmic bands as pathways for the new axons in
the distal stump
EARLY CHANGES IN THE DISTAL STUMP
1. Degeneration of the medullated fibers and the formation of
nucleated protoplasmic bands
Leaving out of account, for the moment, the interesting metamorphoses of the nerve fibers which occur in the distal stump
in the immediate neighborhood of the cut surface during the
first three days, we confine ourselves in this section to the changes
DEGENERATION AND REGENERATION OF NERVE FIBERS 503
which occur at a distance of at least 5 mm. from the end of the
stump. At that distance from the cut surface no changes can
be detected in the medullated fibers in Dog xi, killed one day
after the operation.* The medullated axons still show their
characteiistic, smooth contour and uniform light yellow stain
characteristic of them in their norm.al state. In Dog xii, killed
two days after the operation, many axons have an irregular
surface and are stained more intensely but less uniformly than
normal axons (fig. 1). The same changes are seen in Dog i,
which died about twenty-four hours after the operation. On
the third day, although these changes are somewhat more
advanced, there is as yet no fragmentation of the axons. This
begins on the fourth day and is shown in figure 2. One of the
fibers, a, is broken up into large granules, staining dark brown
and grouped into clumps of irregular size and shape. These
masses are for the most part still connected with each other.
There is a very marked difference in susceptibility of the axons
to degenerative changes. Many of the fibers at this stage are
normal in appearance or are in the stage described as characteristic for the second day. Such a fiber, showing only very slight
alterations, is seen in figure 2, b.
Changes in the myelin sheaths cannot be clearly seen in these
specimens. Howell and Huber ('92) found the first evidences
of segmentation of the mj^elin sheath on the fourth day. It
is therefore plain that granular degeneration of the axons is well
advanced before the segmentation of the myelin sheath begins.
This agrees with the observations of Bethe ('03).
After eight days the first 3 mm. of the distal stump are almost
completely degenerated; the degeneration becomes less and less
marked during the next 2 mm.; and at a distance of 5 mm.
from the cut surface we have a condition which is characteristic
for the remainder of the distal stretch included in the section
(an additional 5 mm.). It is probable that this stage of degeneration would be found throughout all the rest of the distal
portion of the nerve. It is also probable that those who have
described the degeneration as progressing from the point of
injury downward along the nerve have been misled by this rapid
TnE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 6
504 S. WALTER RANSON
degeneration in the first few millimeters of the stump. All
measurements of this sort, referred to in this paper, were made
on longitudinal sections with the aid of the microscope and
mechanical stage. -»
At a distance of 5 mm. from the cut surface eight days after
the operation, the axons of the medullated fibers are broken
up into small irregular clumps of dark brown granules (fig. 3, a).
The myelin sheaths are divided into elliptical segments, separated
and surrounded by the now abundant protoplasm of the neurilemma cells, and containing the granular remains of the axons.
In the preparations of this stage the nuclei are not differentiated, although it is known from the observations of others
that at this time the nuclei of the neurilemma are rapidly increasing in numbers. There are a few medullated fibers whose
axons are not fragmented, but are stained very intensely, have
a fairly uniform contour and an intact myelin sheath. Cajal
('08) has called attention to these resistant fibers. Since there
are all gradations between the most susceptible and the most
resistant, there seems to be involved not a distinction in the
kind of fiber, but in the functional state, nutritive condition,
and vitality of the fiber at the moment of the lesion.
Fourteen days after the operation there are no longer any
unfr?,gmented medullated fibers, although some are in the early
stages of degeneration. In most of the fibers the protoplasm
has increased in quantity and the myelin is divided into droplets, while the remains of the axons are less in evidence. Nineteen days after the operation the protoplasmic bands of Biingner
have made their appearance (fig. 4). The small quantity of
protoplasm surrounding the nuclei in the normal fiber has increased and surrounded the fragments of myelin. And as the
remains of the axon and myelin have been absorbed, this protoplasm has come to fill the old neurilemma sheath. In the meantime the nuclei have increased in number. As a result, we have
a continuous band of protoplasm containing many nuclei (fig.
4, a), and occasional droplets of myelin (6). Scattered through
the remains of the myelin are fine, darkly staining granules
representing the remains of the axon. The protoplasm some
REGENERATION AND REGENERATION OF NERVE FIBERS 505
times appears distinctly striated, as is shown in the drawing
at one end of the band. Such a longitudinal striation has, lead
Biingner, Bethe, and others to suppose that they had before
them the beginnings of a new axon. Even Marinesco ('06)
using Cajal's method was at first led into this error; but later,
perhaps with better preparations, he changed his view and
adopted the conception of the outgrowth of the axon from the
central stump. There are absolutely no transition stages between
such striations and the new axons, which, when they first appear
in the peripheral stump, are sharply defined from all surrounding
structures (fig. 28). Even at' this stage, nineteen days after
the operation, these protoplasmic bands are capable of serving
as paths for the developing axons. A considerable number of
fine black fibers can be seen in the proximal part of this distal
stump. They lie in the protoplasmic bands and run around
the droplets of myelin. These new axons can be followed by
a study of the serial sections back to the scar through which
they have traveled from the central stump.
In Dog X, in which 1 cm, of the nerve was excised, a careful
study of serial sections fails to show any axons which have
pierced the intervening scar and entered the distal stump. In
these preparations, therefore, we are able to study the protoplasmic bands without any complication from ingrowing aions.
The length of time from operation to autopsy in this experiment was twenty-five days. Most of the detritus from the
axons and myelin sheaths has been absorbed, but one sees scattered through the field a few good sized droplets. The protoplasmic bands have assumed a fairly uniform contour and stain
a light yellow. Fine black granules are scattered through the
protoplasm. These are sometimes arranged in parallel rows,
giving a striated appearance. In none of these fibers is there
any indication of the beginning of an axon. This is significant
when taken in connection with the preceding case in which the
two stumps were united, and in which, although the time between
operation and autopsy was six days shorter, new axons could
be seen in many of the protoplasmic bands in the neighborhood
of the scar.
506 S. WALTER RANSON
In the dog which was killed thirty-four days after the removal
of 1 cm. of the sciatic nerve, the distal stump showed protoplasmic bands like those already described except that the droplets of myelin were smaller and scarcer. A few showed new
axons within them; but these axons could be followed for long
distances, were sharply differentiated from the protoplasm of
the band and were connected with fibers in the scar. No transition stages could be seen which might be interpreted as the
development of axons in situ. More will be said about the
relation of the new axons to the protoplasmic bands in the last
section of this paper.
2. Degeneration of the non~medullated fibers and formation of
nucleated protoplasmic hands
So far as we are aware no one has described the degeneration
of the non-medullated fibers of the spinal nerves. Tuckett
('96) presents experiments showing that the sympathetic axons
lose their affinity for methylene blue on the second day after
separation from their cells of origin. Cajal and others who have
used the silver method as he directs have apparently been able
to see these fibers in the spinal nerves only when they were
undergoing regenerative or degenerative changes and possessed
an increased affinity for the silver. Cajal states that he has
followed the degeneration of the non-medullated fibers during
the first eight days, but his observations clearly refer only to
the immediate vicinity of the lesion where the fibers have undergone an abortive regeneration. He states that the centrally
directed end bulbs (which we will describe in another place)
and the non-medullated fibers which carry them, stain well
until the third day, after which they gradually fade out and
are no longer visible after the sixth or seventh day. These
statements are correct only when they are made to apply to
the distal stump within 1 mm. of the cut surface.
At a distance of 5 mm. from the cut surface one day after
the operation. (Dog xi), many of the non-medullated fibers are
no longer uniformly stained but are distinctly granular. At
the end of the second day (Dog xir), the fibers become broken
DEGENERATION AND REGENERATION OF NERVE FIBERS 507
up into segments of varying length. Short, hght segments
alternate with longer, very much darker segments (fig. 5). The
dark segments are granular, a detail which has been omitted in
the. drawing. For control we have the normal nerve from Dog
XI, carried through the same solutions at the same time as the
divided nerves of Dogs xi and xii. As these changes are not
seen in the normal nerve, we may be sure we are not dealing
with artifacts. Three days after the operation, the darker
segments, still granular in appearance, stain less intensely than
in the specimen taken a day earlier. A considerable number of
smooth, black, uniformly stained, non-medullated fibers can be
seen — but these are not so much in evidence as at a later date
when the other fibers have undergone more complete degeneration. Again in this experiment we have the normal nerve
carried through the same solutions at the same time as the
divided nerve, to serve as a control, and show that the described
changes are not artifacts due to an irregular deposit of silver.
Two dogs were killed four days after the operation. Both
showed only a little advance over the specimen taken on the
third day; but many of the fibers are already taking a light
yellow stain with little differentiation into lighter and darker
segVnents.
After eight days many of the non-medullated fibers are no
longer visible, others appear as light yellow bands along which
an occasional nucleus can be seen.
It is at this stage when the other fibers are very lightly stained
or have disappeared that the resistant undegenerated fibers
are most evident. These are more numerous and persist longer
than the resistant medullated fibers. Since the majority of
the non-medullated fibers degenerate very early and since there
are few fibers which show an intermediate degree of resistance,
it is possible that we are dealing here with two different kinds
of fibers. Those which degenerate early in the first week may
be afferent spinal fibers; while those which degenerate in the
second and third weeks may be of sympathetic origin. This
supposition is the more probable because the susceptible fibers
represent about the same proportion, which on other grounds
508 S. WALTER RANSON
we would assign to the class of afferent spinal non-medullated
fibers, while the resistant fibers correspond in number to the fibers
of sympathetic origin. Cajal ('08) in one place called attention
to the slow degeneration of the non-medullated fibers, overlooking entirely the much larger number which degenerate very
early, while in another place in the same monograph he states
that all the non-medullated fibers have disappeared by the sixth
or seventh day.
In Dog V, fourteen days after the operation, the non-medullated fibers are represented by narrow yellow bands stippled
with dark brown fine granules. The nuclei are not differentiated in this preparation. A considerable number of resistant
non-medullated fibers still retain their intense black uniform
stain but they present for the most part an irregular contour
(fig. 6) . Some of these fibers seem to be present after nineteen
days, but in this specimen new axons have grown in from the
central stump and might be confused with persistent axons.
The peripheral stump of the specimen taken twenty-five days
after the operation is not contaminated with new axons from
the central stump and here it can be seen that all the old axons
have degenerated.
In Dog V, nineteen days after the operation, the degenerated
non-medullated fibers are more clearly visible than on the eighth
and fourteenth day, and the nuclei upon them are well differentiated. The fibers are fine yellow bands with many nuclei.
Surrounding many of the nuclei there are considerable accumulations of protoplasm. A short section of three such fibers is
represented in figure 7. The fibers are not interrupted as the
drawing would indicate, but can be followed for considerable
distances even in relatively thin sections. The fibers and the
protoplasm about the nuclei still contain dark brown granules.
After twenty-five days these fibers present the same picture
as in the preceding specimen. They are clearly differentiated
and the nuclei are sharply stained. These fibers are grouped
in bundles and lie between the protoplasmic bands formed by
the medullated fibers, from which they can be distinguished
by their small size and by the absence of myelin droplets.
DEGENERATION AND REGENERATION OF NERVE FIBERS 509
In the preceding paragraphs we have recorded the changes
as they can be observed from day to day in the degenerating
non-medullated fibers. These observations may be summarized
and interpreted as follows. The axons of the majority of the
non-medullated fibers begin to degenerate within twenty-four
hours after they have been separated from their cells of origin.
They first become granular and after two or three days become
broken up into segments of lighter and darker staining. The
darker stained segments represent the fragmented axon, the
lighter segments represent accumulations of unstainable substance probably of fluid character. It is not easy to determine
whether the active process is a vacuole formation with extension in the long axis of the fiber causing separation of the fragments of the axon, or whether a retraction of the fragments
leaves the empty spaces within the neurilemma to be filled with
exudate. On the fourth d-ay the dark segments have begun to
disintegrate and by the eighth day the dark segments have
disappeared, the remains of the degenerated axon are distributed
as brown granules through the probably fluid contents of the
neurilemma sheath. During the next stage, eight to fourteen
daj^s after the operation, the fibers are not very clearly seen.
But by the nineteenth day the nuclei of the neurilemma have
increased greatly in number and the fibers again become clearly
visible, since with the increase in the number of nuclei the protoplasm has also increased and filled in the old neurilemma
sheath. We have, therefore, as the terminal stage of the degeneration of the non-medullated fibers nucleated protoplasmic bands
which differ from the similar bands formed from the medullated
fibers only in size and in the absence of myelin droplets.
In this connection certain observations of Perroncito ('09)
are of great interest. He noticed that in the neighborhood
of the bundles of non-medullated fibers spindle shaped cells
appeared on the third and fourth days and that these became
more numerous on the seventh and eighth days and lay in connection with bundles of connective tissue fibers. He failed
to recognize the formation of the protoplasmic bands from the
medullated fibers and stated that at last ^'in place of the nerve
510 S. AVALTER RANSON
there remains a connective tissue strand consisting of connective
tissue fibers and very long spindle cells." These cells, according to him, arise from the spindle shaped connective tissue
cells which appear between the nerve fibers shortly after division
of the nerve. He adds:
But before we assume that these are true connective tissue cells,
we must seriously consider one objection. We know that between
the medullated nerve fibers there were bundles of non-medullated
fibers. Could not these spindle cells represent cells associated with
the non-medullated fibers and be homologous to the cells of Schwann's
sheath? This objection has, however, many weak points.
It is clear that Perroncito is here describing the same phenomena which we have interpreted as the formation of protoplasmic bands from the non-medullated fibers. His di'awings
show, however, that his preparations clearly differentiated little
more than the nuclei in question. The pyridine-silver preparations, on the other hand, clearly differentiate, not only the
degenerating non-medullated fibers, but also the protoplasmic
bands derived from them.
While a few non-medullated fibers, probably of sympathetic
origin, may persist for two or three weeks, all non-medullated
fibers in the peripheral stump undergo degeneration before the
end of the fourth week. This shows that the direction of Wallerian degeneration is the same for the non-medullated as for
the medullated fibers, and excludes the possibility that any of
them might arise from cells located at the periphery, unless
one cares to consider the very remote possibility that the slowly
degenerating non-medullated axons undergo a cellulipetal degeneration toward peripherally located sympathetic ganglion cells.
3. Abortive autogenous regeneration in the distal siunip
It will be remembered that all the descriptions and drawings
in the two preceding divisions of this paper refer to the distal
stump at a distance of at least 5 mm. from the cut surface. It
was necessary to choose a point at some distance from the cut
surface, because changes occur in the immediate neighborhood
of the lesion which are essentiallv different from those seen in
DEGENERATION AND REGENERATION OF NERVE FIBERS 511
the remainder of the peripheral stretch. These changes have
been described by Perroncito ('05), Poscharissky ('07), and
Cajal ('08), with whose observations our own are in full accord.
These changes begin very early. One day after operation
they are already well adanced in both the medullated and nonmedullated fibers. In the millimeter nearest the cut surface
the non-medullated fibers possess lateral branches, and the
fibers as well as their branches end in bulbs (figs. 8 and 9). The
mode of formation of these branches is the same as the mode
of formation of the similar branches seen in the immediate
neighborhood of the lesion in the proximal stump; but, since
the successive stages are more clearly seen there, we will describe
their formation when describing the central stump. The side
branches are usually as large as the parent stem. The end
bulbs are very characteristic, differing markedly from those
seen on the ends of fibers taking part in the ultimate regenerative changes. These bulbs have a darkly staining core with
a neurofibrillar network, and a peripheral lightly staining zone,
which is often of considerable thickness and shows no visible
neurofibrils. These side branches are so numerous and their
end bulbs so large that they separate widely the original fibers
of a bundle. The last 0.5 mm. of the stump assumes a characteristic appearance under low magnification due to the replacement of the parallel bundles by a network, the individual fibers
of which are separated by large end bulbs. It seems probable
that the outer hghtly staining zone of these end bulbs represents
an excessive accumulation of interfibrillar substance.
The growth of lateral branches and the formation of end
bulbs does not progress much, if any, after the first day, but
remains stationary during the second, third and fourth days.
We have unfortunately no intermediate stages between the
fourth and eighth days, and during this time the products of
this abortive regeneration have almost entirely disappeared.
There are to be seen after eight days shadowy outlines of the
bulbs and a somewhat more definite indication of the branched
fibers. A few of the fibers and end bulbs are still clearly stained.
After fourteen days there are still a few scattered fibers show
512 S. WALTER RANSON
ing end bulbs and one small fasciculus at the periphery of the
nerve in which many well stained side branches and bulbs are
seen. These resistant elements correspond to the central ends
of the resistant non-medullated fibers, which, it will be remembered, retained their staining reaction for a period of two or
three weeks. All of these resistant fibers with the branches
and bulbs at their central ends have entirely disappeared before
the twenty-fifth day and no traces of them are to be found in
the preparation taken on that day.
Changes of the same nature occur in the medullated fibers.
In the immediate vicinity of the lesion (0.5 mm.) many of the
medullated axons present a zone of reaction, which separates
the, as yet, nonnally staining distal stretch, from a very short
disintegrated piece of the axon at the cut surface. This zone
of reaction becomes more marked on the second and third days.
There is almost no limit to the variety of appearances which the
reaction zone may assume; but the fiber illustrated in figure 10
may be taken as showing the principal factors involved. The
myelin sheath in this part of the fiber is already broken up and
appears as granular detritus filling the old sheath. Imbedded
in this mass we have the axon and its products. The central
and peripheral ends of the fiber are marked c and p, respectively. The proximal part of the axon has completely degenerated; fragments of it can be seen at a. At h, the axon shows
a sharply defined club-shaped enlargement which represents
the end of the living part of the axon. Following the axon in
a peripheral direction, one sees at the distal end of the enlargement a distinct neurofibrillar reticulum. Below this the axon
contracts, expands, contracts again and goes over into a second
wider meshed fibrillar reticulum. From both of these reticula
fine black fibrils, d, are given off which run by themselves in
the degenerated myelin. These isolated fibrillar branches are
also seen on the central side of the club-shaped enlargement.
The reaction in the medullated axons therefore consists of (1)
the formation of a distinct line of separation between a short
dead segment and the remaining distal stretch of the fiber,
which is still living, (2) the appearance near this line of separa
DEGENERATION AND REGENERATION OF NERVE FIBERS 513
tion of a distinct neurofibrillar reticulum, and (3) the formation
of fine fibrils which leave this reticulum and run independently
through the degenerated myelin.
The manner of formation of at least some of these independent fibrils is shown in figure 11. In the peripheral part
of the drawing (p) there is a well-marked neurofibrillar reticulum from one side of which there arises a lateral branch ending
in a bulb showing a distinct reticulum. On the central side
this fiber presents two branches c and c' . It is probable that.
c' represents a pre-existing collateral and not a new formed
branch. Most of the fibrils arising from the central end of
the reticulum pass into this branch.
Many, perhaps a majority, of the medullated axons, never
show any of these changes but undergo an uncomplicated degeneration throughout their entire extent. Those fibers which
show no reaction near the lesion represent, in all probability,
the more susceptible fibers, which are well advanced in degeneration throughout their entire extent by the fourth day. The
more resistant the fiber, the more marked is the reaction near
the lesion and the more tardy is the fragmentation of the remainder of the distal stretch. By the eighth day most of the
products of this reaction have disappeared and by the fourteenth
day there are no longer any traces of them.
The changes which have been described in the medullated
and non-medullated axons of the distal stump are without significance for the ultimate regeneration of the nerve, since all
the products of this reaction suffer complete degeneration and
disappear. In themselves, however, these changes are of the
highest interest. They show that that portion of a fiber which
is separated from its trophic center does not die at once. It
continues to live for two or three days and possesses sufficient
vitality to cause a rearrangement of its fibrils into a complicated
reticulum . and to give rise to lateral branches. The presence
in reacting medullated fibers of fine fibers budding off from the
side of a reticulum as shown in figure 11, and the fact that some
of these fine fibers pierce the neurilemma and run out into the
endoneurium can only be interpreted as true branching, although
514 S. WALTER RANSON
it is probable that others of the independent fibrils within the
old sheath have gained their independence by the degeneration
of the fibrils which surrounded them. In the case of the nonmedullated fibers the lateral branches with their end bulbs
constitute the chief evidence of the reaction. One might assume
that the appearance of the neurofibrillar reticulum was only
a peculiar manifestation of degeneration. But the formation
of new branches can only be interpreted as regenerative in character and accepted as evidence that the axons live in the distal
stump for some time after being severed from their trophic
centers. Cajal ('08) places the same interpretation on these
phenomena.
Harrison ('08) found that, after cutting the nerves of the
tail of the larvae of Rana sylvatica, the two cut ends of many
nerve fibers had united by a protoplasmic bridge within one
or two days. In these fibers the degeneration of the peripheral
part of the axon was immediately arrested. These observations find support in the evidence just presented to show that
a portion of an axon severed from its trophic center continues
to live for two or three days.
While Cajal ('08) and others, who have used his method in
the study of the regeneration of nerves, saw and described the
changes in the non-medullated fibers of the distal stump, just
as they have been described here, they leave the impression
that only a few scattering fibers are involved. They seem,
also, to have overlooked the fact that exactly similar changes
occui- in the non-medullated fibers of the proximal stump.
EARLY CHANGES IN THE PROXIMAL STUMP
1 . Changes in the non-medullated fibers
The changes in the non-medullated fibers may be divided into
three stages: (a) early abortive regeneration; (b) cellulipetal
degeneration; (c) the formation of new axons. .
a. Early abortive regeneration. By early abortive regeneration
in the non-medullated fibers of the proximal stump wc mean to
designate a reaction exactly analogous to the abortive regen
DEGENERATION AND REGENERATION OF NERVE FIBERS 515
eration of these fibers in the distal stump. In the last 0.3 mm.
of the proximal stump one sees at the end of twenty-four hours
the formation of lateral branches on the non-medullated fibers.
The stages in the formation of these branches are illustrated in
figure 12. The earliest stage is seen at d, and consists in the
development on one side of the fiber of a spherical mass several
times thicker than the fiber and staining only a trifle less intensely
than the fiber itself. These masses seem to possess the power of
ameboid movement and work their way out of the fiber bundle in
which the}^ orignated, pulling on the fiber and forming a F-shaped
bend in it. Three stages of this are seen at d, c and e. As
the mass moves farther it comes to be connected with the Vshaped bend in the old fiber by a single limb which is formed
behind the mass as it moves forward. Thus the V becomes
transformed into a Y (fig. 12, h). As the lateral branch is formed
it often happens that the distal limb of the V degenerates. The
distal limb of the F in c can be followed only a short distance
when it goes over into a finely granular thread (not shown in
the drawing) and disappears. The fiber and bulb seen at a
are to be accounted for in this way. The bulb appears as if on
the end of a fiber which has turned at right angles and left the
bundle.
The composition of the bulbs on the ends of the lateral branches
varies. At first (fig. 12, c, d, e) the neurofibrillar content is
fine and uniformly distributed, giving to the bulb a stain almost
as dark as that of the, fiber. At this stage the fibrillar plexus
can only rarely be seen. As growth continues the interfibrillar
substance increases greatly in quantity and out of proportion
to the increase in fibrillar substance. This may, in rare cases,
lead to the formation of a wide meshed neurofibrillar reticulum
(fig. 12, h) or more often to the accumulation of a large mass
of lightly staining substance about a central fibrillar core. This
central core is about the size of the original bud from the side
of the fiber.
It should be noted that the bulb shown at h is an exceptional
one in the clearness with which the fibrillar reticulum is stained
and in the fact that it gives off secondary branches. There
516 S. WALTER RANSON
were two of these secondary branches, each ending in a Uttle
ring. More than one lateral branch may be given off from a
single non-medullated fiber. On one fiber two such buds in
the early stages of formation were separated by not more than
twice their own diameter from each other.
These early branches do not appear to develop much after
the first day and on the second day are already overshadowed
by the transformations of the axons of the medullated fibers.
On the third day, coincident with the beginning of a cellulipetal
degeneration in the fibers from which they arose, these branches
and end bulbs become indistinct in outline and begin to lose
their affinity for the stain. And after four days one can distinguish only indistinct shadowy outlines of the bulbs and fibers
(fig. 18, c). These products of the early regenerative activity
of the non-medullated axons in the proximal stump are therefore abortive and very rapidly undergo degneration. It is an
interesting fact that their development in the proximal stump
did not progress as far as that of the similar structures in the
distal stump and underwent degeneration earlier. This early
abortive regeneration is an expression of the local vitality of the
cut fiber just as is that of the peripheral stump. The reason
for the final degeneration of these products is to be found in
the fact that a cellulipetal degeneration occurs in the fibers
from which they arose, thus cutting them off from their connection with the cell body.
b. Cellulipetal degeneration. Coincident with the beginning
of the degeneration of the products of the non-medullated fibers
near the cut surface, changes are noticed in the fibers themselves. These changes, first noticed on the third day, are well
advanced on the fourth and extend up the fibers as far as they
are included in the section. On the eighth day the alterations
in these fibers at various distances from the cut surface (measured with the aid of a mechanical stage) are as follows: In the
last 0.5 mm. there are only a few shadowy outlines of the nonmedullated fibers; at 3 mm. from the cut surface the fibers can
be clearly seen but are in the late stages of degeneration similar
to those in the distal stump, on the same da}^ and at the same
DEGENERATION AND REGENERATION OF NERVE FIBERS 517
distance from the cut surface. From this point to a point at
a distance of 10 mm. from the lesion the intensity of the degeneration decreases until at 10 mm. there are exhibited changes
similar to those seen at the end of the second day in the distal
stump. There are here the same breaking up of the fibers
into light and dark segments and the same granular staining
as has already been described in the distal stump. In the proximal stump, however, there is the important difference that the
intensity of the process decreases rapidly in a central direction;
and although our section, only a little more than 1 cm. in length,
does not permit us to say at just what point the degeneration
ceases, there can be little doubt that it does not extend more
than 2 cm. up the nerve. We are dealing here with a cellulipetal or retrograde degeneration.
A- slow, ascending, cellulipetal, or retrograde degeneration
has been noted in the medullated fibers in cases of long standing amputation (Ranson '06). It is questionable whether such
a degeneration occurs in any of the medullated fibers within
the time covered by this series of experiments; no clear evidence
of its occurrence could be found after thirty-four or thirty-five
days. Its occurrence in the non-medullated fibers is of special
interest since it indicates a greater susceptibility of the neurones, of which they form a part, to lesions of the peripheral
nerve. On cutting the dorsal ramus of the second cervical
nerve in the white rat, near the ganglion, Ranson ('06) noted
that 52 per cent of the cells in the associated ganglion underwent complete degeneration. It was later shown (Ranson '09)
that the cells which disappeared were the small cells, which we
now know to be associated with the non-medullated fibers;
while very few, if any, of the large cells, which are associated
with the medullated fibers, disappeared.
While in those experiments the cut was made very close to
the ganglion, in the present series of experiments the sciatic
was divided at a relatively great distance from the ganglion.
And, following the law that the intensity of the reaction in
the cell depends upon the proximity of the lesion in the axon
to the cell-body, the division of the non-medullated fibers
518 S. WALTER RANSON
in the sciatic involved only a limited cellulipetal degeneration.
While, of course, the usual axonal reaction must have occurred
in the small cells, these did not degenerate. The spinal ganglia
associated with the injured sciatic nerve in Dogs vii and viii,
killed thirty-four days after the operation, and Dogs ix and x,
killed twenty-five days after the operation, were prepared by
the pyridine-silver method. In these ganglia the small cells
and their associated non-medullated fibers were apparently
as numerous as in normal ganglia, although, since no counts
were made, it would be impossible to be sure that none had
degenerated. The non-medullated fibers in the ganglia and
adjacent portion of the nerves stained in a perfectly normal
manner, showing that they were not involved at that level in
a cellulipetal degeneration. Another piece of evidence, showing that the cellulipetal degeneration in the neighborhood of
the lesion did not involve the degeneration of the entire neurone,
is found in the subsequent regeneration of these fibers.
c. Formation of new axons. On the fourteenth day the majority of the non-medullated fibers in the proximal stump are
still in the late stages of degeneration. They appear as light
yellow, delicate bands, closely resembling the early stages of
protoplasmic band formation, in the distal stump. There are
present, however, on the fourteenth day, many sharply stained
black fibers in the bundles of light yellow ones. One bundle,
in which the regenerative changes have gone particularly far,
is seen in figure 13. In a bundle of sharply staining fibers one
sees five end bulbs, three directed toward the periphery, p,
and two towards the center, c. From this time on there is a
constantly increasing number of sharply staining black fibers
in these bundles. On the nineteenth and twenty-fifth days
there are numerous end bulbs and an increasing number of
fine black fibers. After thirty-four days the bundles of nonmedullated fibers in the last centimeter of the proximal stump
are larger and more compact than in the normal nerve; and
these bundles can be traced, in longitudinal sections, out of
the cut end of the nerve into the scar. A cross section of the
stump taken a short distance above the cut at this time shows
a great increase in tho number of these fibei's (fig. 2(5).
DEGENERATION AND REGENERATION OF NERVE FIBERS 519
The interpretation which is to be placed on these observations is as follows: The non-medullated fibers degenerate a
short distance (about 2 cm.) in a central direction and the
degenerated portions undergo the changes looking toward the
formation of protoplasmic bands. But before these are fully
formed the cellulipetal degeneration has been arrested and
regeneration begins. The fibers above the point where the
degeneration ceases begin to grow downward and on their ends
bulbed extremities can be seen. The great increase in the
number of these fibers in the proximal stump near the lesion
indicates that there also are formed lateral branches, although
on account of the compactness of the bundles it has not been
possible to observe the branching directly. Cajal describes
and figures the branching of non-medullated fibers in the proximal stump, but it seems probable that he was dealing, not with
the original non-medullated fibers but with new axons, which
had branched off from the medullated fibers (fig. 22). The
new non-medullated axons follow the old fiber bundles as pathways and at the cut end of the nerve they finally reach the scar,
into which they ran.
2. Early changes in the medullated axons of the proximal stump
a. Formatio7i of a zone of reaction. In the immediate neighborhood of the lesion one sees changes in some medullated axons
that greatly resemble those seen at an early stage in the distal
stump. Figure 14 represents a typical fiber of this sort at the
end of the first day. At d one sees the axon staining like the
normal axon a light yellow; but it is beginning to increase in
diameter. As we follow it from the central (c) toward the
peripheral end (p) it increases in size and assumes a darker
stain. At the same time, indications of a neurofibrillar reticulum make their appearance. At b the axon is several times
its normal thickness, filling and distending the neurilemma.
It shows at this point, and for a short distance above, a dense
deeply staining reticulum. This corresponds to the club-like
zone of reaction seen in figure 10, except that the neurofibrillar
reticulum is more pronounced. At a the disintegrated remains
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 6
520 S. WALTER RANSON
of the axon can be seen and this degenerated stretch extends
to the cut surface 0.2 mm. distant. As can be seen, there is
not a. very sharp border between the degenerated portion of
the axon and the zone of reaction. Isolated portions of the
reticulum extend into a lightly stained intermediate zone. At
a, the neurilemma can be seen; at h, it is stretched over the
swollen axon and is not differentiated, while at c, both the neurilemma and myelin sheath can be seen in the preparation but
were not indicated in the drawing. More rarely one sees two
dense fibrillar reticula, separated by a zone of light staining
through which run a few connecting fibrils.
h. Fibrillar dissociation. In many axons there occurs a separation of the neurofibrils due to accumulation of an excess of
interfibrillar substance, and at the same time the individual
fibrils become much more sharply stained. This process occurs
alike in fibers which have formed a zone of reaction and in those
which have not. Figure 15 represents a short stretch of an
axon 0.5 mm. from the cut surface two days after the lesion.
On following this axon toward the cut surface it is seen to go
over into a narrow band of fibrils which connect it with a zone
of reaction near the lesion. Between the part of the axon,
which was drawn, and the zone of reaction there is a stretch of
about 0.2 mm. in which most of the axon is fragmented and
only a narrow band of fibrils connects the two. The accumulation of interfibrillar substance seems to be more abundant on
one side of the axon where large spaces are present between the
fibrils. There does not seem to be any new formation of fibrils
and only such rearrangement as would naturally take place
in case of an oedematous swelling of the axon. It will be noticed
that the network is most dense at the periphery of the axon.
When this process is carried to its full extent, as one sometimes
sees it on the second, third and fourth days, the axon becomes
converted into a fine meshed network forming a hollow cylinder.
The myelin sheath having disintegrated, this net-like cylinder
lies immediately beneath the neurilemma. These appearances
would, of course, be best understood on the hypothesis that
the fibrils of the normal axon are not isolated but are united
DEGENERATION AND REGENERATION OF NERVE FIBERS 521
with each other to form a network, the meshes of which are
drawn out in a longitudinal direction.
c. Early branching of axons in the immediate neighborhood of
the lesion. The fibers which give rise to these branches undergo
no degeneration at the point of division nor do they form at
their cut extremity a darkly staining zone of reaction. We
are dealing here with fibers which either possessed a greater
vitality or were less severely traumatized in the cutting of the
nerve. There seem to be two chief modes by which the branches
arise from these fibers:
1, Some of these fibers begin to grow distally very soon after
the lesion and by the end of the first day have grown out of
their sheaths into the exudate. Here they immediately break
up into a great number of fine branches. Figure 16 represents
two such fibers one day after the operation. At c and c' they
are leaving their sheaths and growing into the exudate. A
large fusiform lateral branch is given off from one of the fibers.
This large lateral branch, .as well as the two main fibers, show
the neurofibrils very clearly — these fibrils are however more
nearly parallel in their arrangement and not so closely set as
in the zone of reaction shown in figure 14, b, and on the whole
give the ends of the fibers a much more normal appearance.
At many points these axons give off fine fibrillar branches which
end in small cylindrical or spherical expansions. In the surrounding exudate there are numerous isolated rings which represent cross sections of the expanded ends of other fibers. This
is a very characteristic ending for the fine branches of the medullated axons at this stage — an elongated club-shaped end bulb
whose fibrillar substance is located at the periphery, in cross
section appearing as rings and in longitudinal section as hollow
clubs.
2. Instead of arising from the ends of axons, extremely fine
side branches may arise from the surface of the axon within
its sheath. Axons giving rise to branches of this sort show no
degenerated stretch near the lesion nor any dark zone of reaction. They show however a certain amount of fibrillar dissociation in that the axons are swollen and the fibrils are much
522 S. WALTER RANSON
more sharply differentiated than in normal axons. Some of
these fibrils detach themselves from the axon at its surface
to form fine branches, which run in various directions on the
surface of the axon and after a short course end in small bulbs
(fig. 17). Some of these branches, which arise near the cut
surface find their way out into the exudate, but most of them
continue to grow within the old sheath. In the absence of the
myelin sheath, which is entirely disintegrated in these last few
tenths of a millimeter of the proximal stump, these branches
reach the neurilemma and immediately underneath this they
continue to grow in a circular or spiral direction, interlacing
with one another. In this way there develops by the third or
fourth day, just beneath the neurilemma, a hollow cylinder
formed by fine interlacing fibers, within which the old axon can
be seen (fig. 18, a, 6). Many of these fine fibers can be seen
ending in little rings. While the majority of them remain
within the old neurilemma sheath, a few, leaving it at the cut
surface, run into the exudate and a few others, piercing the
sheath, run into the eudoneurium.
'In figure 19 the axon is seen giving off some relatively coarse
branches, some of which have arranged themselves in a tubular
sheath. The axon and part of the sheath are cut away in one
place, where they run out of the section.
In some of the medullated axons the fibrillar dissociation
represented in figure 15 and the branching illustrated in figure
17 seem to be associated in the production of a tubular network.
Sometimes the central axon can be seen to break up into this
network and be reformed from it again at a lower level.
The formation of a zone of reaction, the fibrillar dissociation,
and the formation of the early collateral branches within the
old neurilemma sheath, together with the tubular networks
which have just been described, constitute the early changes
in the medullated axons which were first seen by Perroncito
and which Cajal has called Perroncito-phenomena. On the
eighth, fourteenth and nineteenth days all of these structures
become less and less evident, and their place is taken by parallel coursing fibers, of which there are a large number within
DEGENERATION AND REGENERATION OF NERVE FIBERS 523
the remains of one old neurilemma sheath. The steps in this
substitution are not clearly presented in the preparations studied. But it seems probable that some of the fibers of the network atrophy and that others assume a more parallel course.
It is certain that many branches arise from the axons at a slightly
higher level and, growing down within the neurilemma sheaths,
help to take the place of the disappearing network. It is obvious that these plexuses, as such, take no part in the final regeneration, although individual fibers, derived from them, may do
so. Nineteen days after the operation none of the old networks are to be seen; but instead, only parallel coursing fibers,
branching fibers and twining fibers held together in bundles
by the old neurilemma sheaths. All of these earliest phenomena
are confined to the last few tenths of a millimeter of the proximal stump.
d. Formation of lateral branches at some distance above the
lesion. On the eighth day, when the tubular arrangement just
described has begun to disappear, one sees that the medullated
fibers are giving off lateral branches at a higher level. These
are of good size and can be seen coming off as high as 5 mm.
above the cut. These side branches become more and more
abundant in each of the three succeeding stages, fom'teen, nineteen, and twenty-five days after the operation. On the nineteenth day, they can be seen in large numbers (fig. 20) chiefly
in the terminal 5 mm. of the nerve. They end in bulbs and
usually run within the old sheath, predominantly in a peripheral
direction, but some run spirally, and others centrally, in the
old sheath, and still others pierce the sheath and run in the
endoneurium. In figure 21 one sees a bundle of fibers formed
in this way within an old sheath. The old axon is thicker,
lighter and more centrally placed than its branches which are
accompanying it toward the periphery. Two of these branches
are seen to end in bulbs directed peripherally. Two fine fibers
leave the sheath and run in the endoneurium. One branches
a second time in the connective tissue and the resultant fibers
run out of the section. The other turns peripherally parallel
to and just outside the old sheath and ends in a large end bulb.
524 S. WALTER HANSON
After thirty-four days all the medullated fibers in the last
5 mm. of the proximal stump are transformed into bundles of
fibers in this way. In Dog viii, in which the nerve was sutured
and in which therefore the chemiotactic influence of the distal
stump was brought into full action on the growing fibers of the
proximal stump, most of the newly formed axons grow directly
downward into the scar. As is shown in figure 23, the fiber
bundles are composed of more or less parallel fibers. In Dog
vii, however, where a piece of nerve was resected and the influence of the distal stump therefore was less potent in controlling
the course of the growth of fibers in the central stump, there
are more recurrent fibers. Some fibers instead of passing directly
down the old sheath grow in a spiral direction beneath the old
neurilemma, producing tangled skeins like that illustrated in
figure 24, b. The medullated fiber (a) has been transformed
into a bundle of parallel fibers. These structures are seen in
cross section in figure 25. In all these bundles and skeins, bulbs
on the ends of individual fibers are seen and form a prominent
part of the picture. These two bundles in figure 24 lie side
by side in the preparation and a small group of fibers can be
seen leaving Bundle a and running into Bundle b. While therefore on the whole such a bundle represents the branches of one
old axon, branches may grow from one bundle into another or
from a bundle into the endoneurium. Both recurrent fibers
and tangled skeins are also seen in smaller numbers in Dog
VIII where union of the cut ends favored the action of the chemiotactic influences from the distal stump on the growing axons.
Fibers with bulbous extremities are very numerous in these
bundles and skeins. These end bulbs form a prominent part
of the picture in all the preparations where regenerating axons
are seen. Cajal has correctly interpreted them as analogous
to the enlarged extremities seen by many observers on the ends
of developing nerve fibers and hence they may be regarded as
the growing tips of the axons.
Cajal believes that the tangled skeins arise from the tubular
networks which appear shortly after the lesion. This, however, does not seem to be the case. TKey arise from the lateral
DEGENERATION AND REGENERATION OF NERVE FIBERS 525
branches given off from the axons at a later date and at a higher
level. When these branches instead of growing in a peripheral
direction, coil spirally beneath the neurilemma or turn backward in a central direction, they produce the tangled skeins.
These skeins are seen in the process of formation on the twentyfifth day at a time when all of the tubular networks have disappeared and are often seen farther up the nerve than the level
at which the tubular networks appeared." The fact that they
are more abundant, when the union of the cut ends is prevented,
is readily explained by the less potent attraction exerted on
the growing branches by the distal stump, but would not be
explained by Cajal's hypothesis.
Cajal is of the opinion that the normal mode of regeneration
of the medullated axons consists of the three following stages:
(1) degeneration of a short stretch of the axon near the cut surface; (2) the formation of a bulb on the axon above this stretch;:
and (3) growth of the axon out of the sheath into the scar where
branching occurs. This sequence of events occurred in few,
if any, of the fibers in our sections. In our preparations the
essential factor in the regeneration of the medullated axons of;
tl;e proximal stump was the formation of lateral branches at a;
distance of 1 to 5 mm. above the cut surface and within the old
sheaths, within which they grew peripherally until they reached ,
the scar. The fact that Cajal worked chiefly with young dogs
and rabbits, while this work has been done on adult dogs is
sufficient to explain this difference in the results.
The recent statements of Dominici ('11) that no new axons:
can be observed growing out of the proximal stump during the
first month are not supported by an account of detailed observations, and his negative results are clearly due to an inadequate technique. • ; ;
MECHANISM OF THE REGENERATION OF NERVE FIBERS
We hav6 been concerned in the preceding sections of this
paper with a variety of changes occurring in the proximal and
distal stumps, many of which, so far as we can see, take no
526 S. WALTER RANSON
part in the ultimate regeneration of the nerve fibers. It is our
purpose in this section to trace the steps in the formation of
the regenerated axons, restating briefly those observations
ah'eady mentioned which are of significance in the final process
and linking them together in a coherent whole.
1. Proliferation of axons in the central stump
On the first day after the lesion some of the axons grow out
into the exudate and break up into many branches (fig. 16).
Others on the first day give off fine branches from their surface
within the sheath in the immediate neighborhood of the lesion
(fig. 17), some of which find their way into the exudate. Thus,
from the end of the first day on, fine nerve fibers, which are
demonstrably branches of the medullated axons of the proximal
stump, are present in the developing scar. The chief contribution to the new axons, which enter the scar from the cut end
of the proximal stump, comes from the branching of the old axons
at a somewhat later date (fig. 20). These side branches from
the medullated axons are given off chiefly in the last 5 mm. of
the proximal stretch; and, while a few are formed as early as
the eighth day, they are constantly increasing in number to
the thirty-fourth day. Running for the most part within the
sheath of the old axon from which they arose, they arrange
themselves into fascicles of parallel threads (fig. 24, a) when
their course toward the periphery is direct, and into tangled
skeins (fig. 24, b) when for any reason they fail to grow directly
toward the periphery. Some idea of the enormous number of
such branches can be obtained from a study of cross sections
of the proximal stump just above the lesion (fig. 25). Thus
within the space formerly occupied by one fiber there may be
fifty or even more. These bundles of fine fibers, derived as
branches from the old medullated axons, run compactly until
they leave the old sheath and plunge into the scar. Here they
scatter out in every direction. Some of these fibers never reach
the scar but turn backward in the proximal stump. Whereever it is possible to see these fibers ending within the thickness
of a section they are tipped with a Ijulb.
DEGENERATION AND REGENERATION OF NERVE FIBERS 527
In the case of the non-mediillated axons, which after an abortive regeneration undergo a celluhpetal degeneration for something more than one centimeter up the proximal stump, true
regeneration begins about the fourteenth day. There occurs
a downgrowth of new axons from above the point where the
degeneration ceased. These new axons, on the growing ends
of which small bulbs can be seen, grow toward the cut surface
in the degenerated bundles. These new axons continue to
increase in number until by the thirty-fourth day the bundles
of non-medullated fibers in the last part of the proximal stump
are larger and more compact than in a normal nerve. Although,
because of the smallness of these fibers and the compactness
with which they are grouped, it is not possible to demonstrate
the occurrence of lateral branches on these fibers, there can
be no doubt but that they have increased greatly in number.
This is evident in the longitudinal sections, but even more so
in transverse sections taken a short distance above the lesion
(fig. 26, a). Here one sees large bundles of non-medullated
fibers so closely grouped as to resemble a sympathetic nerve.
Compare this drawing with figure 25 taken at a lower level and
showing the multiplication of the branches of the medullated
fibers. It will be seen that the medullated fibers in the neighborhood of the non-medullated bundles in figure 26 have not
yet begun to give off branches. Hence the large increase in
the non-medullated fibers cannot be due to the side branches
of the medullated fibers growing into the bundles of non-medullated fibers. These bundles can be traced to the end of the
central- stump, where they go over into the scar intermingling
with the branches of the medullated fibers from which they can
no longer be distinguished.
This enormous increase in the number of fibers in the terminal part of the proximal stump is one of the most striking observations that have been made on these preparations — and it seems
to the writer one of the most significant for the interpretation
of the nature of the regenerative process. It fits logically into
the scheme of the outgrowth theory. As we shall see, a great
number of fibers fail to find their way through the scar to the
528 * S. WALTER RANSON
more favorable pathway formed by the distal stump, and the
large number of branches increases the probability that at least
one branch will reach that pathway and develop into a functional fiber. This multiplication of branches is, then, a means
for compensating the loss of fibers in the scar. That more
than one branch of a fiber of the central stump may make such
connections and develop into a functional fiber is shown by
the physiological experiments of Osborne and Kilvington ('08),
who showed that when the peripheral stumps of the tibial and
peroneal nerves were united with the central stump of the tibial
nerve, and regeneration had taken place, it was possible by
stimulating the peripheral end of the peroneal to obtain contractions in the muscles supplied by the tibial. These contractions could still be obtained after the tibial nerve had been
divided above the point of the previous union, thus showing
that some motor fibers in the central stump of the tibial had
sent at least one branch into each nerve.
It seems probable, however, that at best only a few of the
many branches of a central axon make connections with the
distal stump and that the rest atrophy and disappear.
2. Penetration of the scar and loss of fibers
It is in the tracing of these new-formed fibers through the
scar and into the distal stump that the study of the serial sections, in their serial order, was found of most advantage, since
in them it was possible to demonstrate very convincingly the
origin and course of these fibers.
As has been stated, the first nerve fibers make their appearance in the exudate on the first day. These ai;e the fine nonmeduUated branches of the medullated fibers (fig. 16). No
nerve fibers at any time grow out into the exudate or scar from
the distal stump. After the first day little progress in the outgrowth of fibers is made for several days. A few fibers can be
seen in the immediate neighborhood of the central stump on
the second, third and fourth days, but in number and length
they are not much in advance of those seen on the first day.
This temporary arrest of the outgrowth of fibers is probably
DEGENERATION AND REGENERATION OF NERVE FIBERS 529
associated with the violent reaction going on in the neurone at
that time — the so-called 'axonal reaction.'
Unfortunately the eight-day specimen was divided into proximal and distal stumps by a cut through the scar near the cen-,
tral end before the tissue was prepared by the p\'ridine-silver
method; and, as a result, the stain of the central portion of the
scar is not good. On the fourteenth day, however, the scar
is beautifully stained and fibers can be seen in large numbers
leaving the central stump, plunging into the scar, and running
through it in every direction. The same is true of the nineteen-day specimen. Here many fibers are seen working their
way centrally in the thickened perineurium of the central stump
in which they form a plexus connected with the plexus in the
scar. These represent a portion of the aberrant branches that
never find their way into the distal stump. Where fibers are
seen to come to an end within the thickness of a section, they
are tipped with a small bulb. On the twenty-fifth day (Dog
X, in which union of the stumps was prevented by excision of
1 cm. of the nerve) the mass of scar tissue covering the end of
the proximal stump is penetrated in every direction by these
fine nerve fibers; from this mass covering the end of the central
stump, they can be followed in gradually decreasing numbers
upward in the thickened perineurium for 4 mm. and distalward in the scar for a distance of 13 mm. As one goes distally
in the scar the number of fibers gradually decreases. No fibers
reach the distal stump, and no fibers grow into the scar from
the distal stump.
Figure 27 is drawn from the scar in the immediate neighborhood of the central stump of the specimen just described. It
will be noticed that the fibers are arranged in bundles. The
explanation of the formation of these bundles is the stereotropism demonstrated by W. H. and M. R. Lewis ('12) in growing
fibers. When the growing tip of one fiber comes in contact
with another fiber, it follows this second fiber just as, in the
experiments of the authors just mentioned, growing fibers run
along the under surface of the cover glass. It will be further
noted that the bundles, while crossing each other in a more or
530 S. AVALTER RANSON
less irregular manner, run, for the most part, in a general direction from center (c) to periphery (p). This predominant direction is due to the chemiotactic influence exerted upon the growing fibers by the distal stump. There are in the field three
branching fibers (a). Notice that in each case the centrally
directed limb of the Y is the thickest fiber, while the two peripherally directed limbs are thinner, and represent the branches.
Had these fibers arisen in situ, the branching fibers would in
themselves be difficult to account for; but the fact that the
central limb of the Y is almost always the largest of the three
would be even harder to explain. There are no end bulbs represented in the drawing, and in fact there are few in this region.
This is the oldest portion of the nerve plexus in the scar and the
fibers are already of great length and few can be seen having
a true termination within the thickness of a section. As one
approaches the distal extremity of this plexus, 9 to 13 mm.
from the central stump, these end bulbs become relatively much
more numerous, since we are dealing here with the growing
ends of the fibers. Often in the place of an end bulb one sees
the end of a fiber breaking up into a large number of fine branches.
It is an interesting fact that the farther distally in the scar the
plexus goes the more parallel its fibers become, and the more
directly they run toward the distal stump. This is explained
by the fact that the earliest fibers penetrate the scar at a time
when the distal stump has not undergone the alteration necessary for the exercise of the chemiotactic influence and their
direction is very irregular. These early fibers by stereotropism
govern the direction of the bundles. On the other hand, the
early fibers in the distal portion of the plexus are from the first
under the chemiotactic influence of the distal stump which is
stronger because of the proximity of the distal stump.
Dog VIII, killed thirty-four days after the operation, serves
as a good illustration of a scar when the two ends of the nerve
have been sutured. The suturing was not well done and a gap
of some size between the two stumps was filled with scar tissue.
Into this scar the fibers from the central stump can be followed.
The fiber plexus in the scar is very much Uke that in Dog x.
DEGENERATION AND REGENERATION OF NERVE FIBERS 531
But in this case the plexus, composed in its distal part of fairlyparallel fibers, is directly connected with the distal stump into
which the bundles run in great numbers.
While of course it is not possible to follow individual fibers
out of the central stump through the scar and into the distal
stump, yet by a study of serial sections of different stages, it
is possible to convince oneself that all the nerve fibers in the
scar are outgrowths of central axons.
3. The utilization of the protoplasmic bands as pathways for the
new axons in the distal stump
We have already described in the distal stump the multiplication of the nuclei of the neurilemma, the increase of the protoplasm which surroimds them, and the formation from these of
nucleated protoplasmic bands. These bands are formed as the
final stages in the degeneration of both medullated and non-medullated fibers. In none of the specimens was it possible to see any
indications of the development of axons in situ. Occasionally one
sees in them a pseudo-striation due to longitudinal rows of granules, but there are no transition stages between these and the
sharply stained, regenerated axons. Negative results of this
sort, obtained from preparations which sharply differentiate
the finest branch of an axon, are in themselves of great significance. But even more important is the evidence of the direct
growth into these protoplasmic bands of the fine nerve fibers
of the scar.
In Dog V, killed fourteen days after the operation, and Dog
VI, killed nineteen days after the operation, in both of which
the cut ends of the nerve were united by sutures, nerve fibers
had entered the distal stump from the scar. In the nineteenday specimen they can be seen to run into the protoplasmic
bands; but in the fourteen-day specimen these bands are not
sufficiently well developed to permit one to say whether the
new axons have entered these developing bands or not. In
Dog X, killed twenty-five days after excision of 1 cm. of the
nerve, the band fibers are well developed and clearly differentiated, but there is no trace of a new axon in the scar covering
532 S. WALTER R ANSON
the end of the distal stump, nor in the protoplasmic bands.
Their absence in this case, twenty-five days after the operation,
although well developed protoplasmic bands are present, and
their presence in other specimens, fourteen and nineteen days
after the operation when the protoplasmic bands are only incompletely formed, speaks strongly against their development
in situ in these bands. Moreover, in both the fourteen- and
nineteen-day specimens, nerve fibers from the central stump
had reached the distal stump through the scar.
Probably the most instructive preparations, however, are
those from Dog vii, killed thirty-four days after the removal
of 1 cm. of the sciatic nerve. A study of serial sections shows
that the scar covering the distal stump is devoid of nerve fibers
except in one very limited area — here there are a few fibers.
All of the protoplasmic bands in this specimen are devoid of
new axons except a few in that part of the distal stump overlaid by the innervated portion of the scar. Here a few of the
bands can be seen containing sharply staining axons. Figure
28 shows five bands in this location, down one of which a new
axon is growing. The axon can be seen to end in an enlargement directed distally. The presence of a few of these sharply
staining axons in protoplasmic bands adjoining the only part
of the scar which contains nerve fibers, while all the rest of the
bands are empty, is a strong point in favor of their growth into
the distal stump from central fibers. The presence of end bulbs
like .the one seen on the fiber in figure 28 is evidence in the same
direction.
Cajal lays stress on the occurrence of branching in the axons
in the protoplasmic bands. Such branching has been observed
occasionally in these preparations, but its value as an evidence
of the down-growth of the axons seems to the present writer
not to be very great.
In Dog VIII, killed thirty-four days after section of the sciatic
with primary suture, great numbers of fibers from the scar run
into the distal stump. Several axons often run down one protoplasmic band. Figure 29 represents a cross section of this
distal stump. At a is seen a large protoplasmic band (formed
DEGENERATION AND REGENERATION OF NERVE FIBERS 533
from a meduUated fiber) containing five new axons, and at h
a bundle of fine protoplasmic bands (formed from non-medullated fibers), in several of which new axons have appeared.
All new axons lie in protoplasmic bands, never between them.
It has been supposed by others that the axons may run between
the bands as well as within them. This appears to be the case
in longitudinal sections; but in cross sections one always sees
the light yellow protoplasm of a band surrounding every axon.
About some of these axons a faint halo of myelin is deposited
b}^ the thirty-fourth day.
No cases were studied in which sufficient time had elapsed for
the complete regeneration of the nerve. We expect to make
other experiments on young dogs with a view to determining
the structure of a fully regenerated nerve and especially the
relative proportion of meduUated and non-medullated axons
which it contains.
SUMMARY
1. The idea, first clearly stated by Biingner, that the new
axons arise in the protoplasmic bands through a fusion of longitudinal striations which have developed in situ, has been shown
by the application of the Cajal stain to be without foundation.
The axons, when they first make their appearance in the distal
stump, are fully developed and clearly differentiated from the
surrounding protoplasm. They do not appear as discontinuous
fragments, but as long fibers, which, when traced peripherally,
may either run out of the section or end within a protoplasmic
band with a terminal bulb, and when traced centrally either
run out of the section or into a plexus of axons in the scar. In
these findings all recent investigations agree. Perroncito ('05),
Maiinesco ('06), Poscharissky ('07), and Cajal ('08), who have
used the Cajal stain, Pupura ('01) with Golgi stain, and Krassin
('06) with methylene blue, have all reached the same conclusion. Their results are in full accord with those of the present
investigation. Even Bethe ('07) is silent on the question of
the histogenesis of the regenerated axons in the distal stump,
since in his last article he makes no attempt to defend his former views on this subject.
534 S. WALTER RANSON
2. The attempts to obtain regeneration in a peripheral stump
permanently separated from the spinal cord and spinal ganglia
have led to negative results. So great is the regenerative energy
of the central stump in young animals that the new axons to
which it gives rise may bridge very great gaps to reach the distal stump; and new axons may grow into that stump from other
nerves. Bethe's elaborate precautions to prevent such union
have clearly not been adequate, as is shown by the experiments
of Langley and Anderson ('04) and Lugaro ('05). Nothing
short of the complete removal of the entire lupibo-sacral spinal
cord with the associated spinal ganglia can be regarded as effectually preventing such reunion and these experiments have
been negative. Since, however, such experiments are open
to the objection that the high grade of marasmus caused by
such an operation could in itself be sufficient to account for
negative results, no very valuable evidence is likely to be furnished by this line of experimentation. Since we now have,
in the Cajal method, a technique which enables us to see clearly
how regeneration occurs when the two ends of the nerve are
allowed to unite, there ceases to be any reason for attempting
to secure an isolated stump. It is highly improbable that there
would occur in such an isolated stump a process essentially different from that which occurs when the two ends are allowed
to unite.
3. It can be shown by the Cajal stain that the axons of both
medullated and non-medullated fibers in the central stump
give rise to a large number of branches which make their way
through the scar and enter the protoplasmic bands, which they
utilize as pathways toward the periphery. Perroncito, Marinesco and Cajal have reached these same conclusions on facts
similar to those presented in the preceding sections of this paper.
Poscharissky, whose observations agree with those of the others,
hesitates to draw any conclusions. The facts upon which the
conclusions just mentioned are based have already been summarized under the heading The mechanism of the regeneration of nerves."
DEGENERATION AND REGENERATION OF NERVE FIBERS 535
4. The axons of the peripheral. stump do not die at once after
the division of the nerve, but hve for two or three days at least,
and undergo changes in the neighborhood of the lesion which
must be regarded as an abortive regeneration. After a few
days all the newly formed structures degenerate and disappear.
This abortive regeneration has no significance for the ultimate
regeneration of the nerve and is of interest only because of the
hght it throws on the life processes within the neurone. These
phenomena, first seen by Perroncito, have been fully confirmed,
not only in the present investigation, but also by Poscharissky,
Marinesco and Cajal.
5. Alterations in the axons of the proximal stump can be
noticed within twenty-four hours after the lesion. They consist of the formation of fine branches, and the rearrangement
of the neurofibrils of the old axons to form the most complicated networks. These changes are limited to the immediate
neighborhood of the cut surface and are too varied to summarize in detail. These were also first seen by Perroncito and confirmed by the~ others who have used the Cajal technique.
6. The new observations presented in this paper concern
almost exclusively the non-medullated fibers which are now
known to outnumber the medullated fibers in the spinal nerves.
These observations have been summarized in the section on
"The mechanism of the regeneration of nerves."
BIBLIOGRAPHY
Ballance, C. A., AND Stewart, P. 1901 Cited after Cajal.
Bethe, A. 1903 Allgemeine Anatomie iind Physiologie des Nervensystems.
Leipzig.
/ 1907 Neue Versuche iiber die Regeneration der Nervenfasern. Archiv
f. d. Gesam. Physiol., Bd. 116, p. 385.
BtJNGNER, O. V. 1891 Ueber die Degenerations- und Regenerationsvorgiinge
am Nerven nach Verletzungen. Betr. z. path. Anat. u. z. allg. Path.,
Bd. 10, p. 321.
Cajal, Ram6n y. 1908 Nervenregeneration. J. A. Barth. Leipzig.
DoMiNici, M. 1911 Experimenteller Beitrag zum Studium der Regeneration
der peripheren Nerven. Berl. Klin. Wochensch., Bd. 48, p. 1937.
Durante, G. 1904 A propos de la theorie du neurone. Rev. Neurol., vol.
12, p. 573.
THE JOURNAL OF COMP.\RATIVE NEUROLOGY, VOL. 22, NO. 6
536 S. WALTER RANSON
Fleming, R. A. 1902 Cited after Cajal.
Frossman, J. 1898 Ueber die Ursachen, welche die Wachsthumsrichtung der
peripheren Nervenfasern bei der Regeneration bestimmen. Beitr.
z. path. Anat. u. z. allg. Path., Bd. 24, p. 56.
Galeotti, G., and Levi, G. 1895 Ueber die Neubildung der nervosen Ele
mente in dem wiederzeugten Muskelgewebe. Beitr. z. path. Anat.
u. z. allg. Path., Bd. 17, p. 369.
Harrison, R. G. 1908 Regeneration of peripheral nerves. Anat. Rec, vol.
1, p. 209.
Head, H., and Ham, C. S. 1903 The process that takes place in a completely
isolated sensory nerve. Jour, of Phys., Lond., vol. 29, p. vi.
Howellj W. H., and Huber, G. C. .1892 A physiological, histological and
clinical study of the degeneration and regeneration in peripheral nerve
fibers after severance of their connection with the nerve centers. Jour.
of Phys., Lond., vol. 13, p. 335.
Huber, G. C. 1895 A study of the operative treatment for loss of nerve substance in peripheral nerves. Jour. Morph., vol. 11, p. 629.
Kennedy 1897 Cited after Bethe, 1903.
Krassin, p. 1906 Zur Frage der Regeneration der peripheren Nerven. Anat.
Anz., Bd. 28, p. 449.
Langley, J. N., AND Anderson, H. K. 1904 On antogenetic regeneration in
the nerves of the limbs. Jour, of Phys., Lond., vol. 31, p. 418.
Lewis, W. H., and Lewis, M. R. 1912. The cultivation of sympathetic nerves
from the intestine of chick embryos in saline solutions. Anat. Rec,
vol. 6, p. 7.
LuGARO, E. 1905 Zur Frage der antogenen Regeneration der Nervenfasern.
Neurol. Centralb., Bd. 24, p. 1143.
]\L\RiNEsco, G. 1905 Recheres sur la regenerescence antogene. Rev. Neur.,
vol. 13, p. 1125.
1906 Etudes sur le mechanisme de la regenerescence des fibres ner
veuses der nerfs peripheriques. J. f. Psy. u. Neur., vol. 7, p. 140.
Marinesco, G., and Minea, J. 1910 Nouvelles recherches sur I'influence
qu'exerce I'ablation du corps thyroide sur la d6g6nerescence et la
regenerescence des nerfs. Compt. Rend. Soc. de Biol. Paris, vol.
48, p. 188.
Modena, G. 1905 Die Degeneration und Regeneration des peripheren Nerven
nach Losion desselben. Arbeiten a. d. Neurol. Inst. Wien. Univ.,
Bd., 12, p. 243.
MoTT, F. W., Halliburton, W. D. and Edmunds, A. 1904 Regeneration of
nerves. Jour, of Phys., Lond., vol. 31, p. vii.
MttNZER, E. 1902 Giebt es eine autogenetische Regeneration der Nervenfasern? Neurol. Centralbl., Bd. 21, p. 1090.
Osborne, W. A., and Kilvington B. 1908 Axon bifurcation in regenerated.
nerves. Jour, of Phys. Lond., vol. 38, p. 268.
Pbrroncito, A. 1905 Cited after Cajal.
1908 Zur Frage der Nervenregeneration. Beitr. z. path. Anat. u. z.
allg. Path., Bd. 44, p. 574.
DEGENERATION AND REGENERATION OF NERVE FIBERS 537
Perroncito, a. 1909 tjber die Zellen beim Degenerationsvorgang der Nerven.
Folia Neuro-biol., Bd. 3, p. 185.
PoscHARissKY, J. 1907 tJber die histologischen Vorgange an den peripher
ischen Nerven nach Kontinuitatstrennung. Beitr. z. path. Anat. u. z.
allg. Path., Bd. 41, p. 52.
Purpura 1901 Cited after Cajal.
Raimann 1905 Discussion of paper by Marqulies. Neurol. Centralbl., Bd. 24,
p. 1015.
Ranson, S. VV. 1906 Retrograde degeneration in the spinal nerves. Jour.
Comp. Neur., vol. 16, p. 265.
1909 Alterations in the spinal ganglion cells following neurotomy.
Jour. Comp. Neur., vol. 19, p. 125.
1911 Non-meduUated nerve fibers in the spinal nerves. Am. Jour.
Anat., vol. 12, p. 67.
1912 The structure of the spinal ganglia and of the spinal nerves.
Jour. Comp. Neur., vol. 22, p. 159.
Segale 1903 Cited after Cajal.
Stroebe, H. 1893 Experimentelle Untersuchungen iiber Degeneration und
Regeneration peripherer Nerven nach Verletzungen. Beitr. z. path.
Anat. u. z. allg. Path., Bd. 13, p. 160.
1895 Die allgemeine Histologic der degenerativen und regenerativen
Processe im centralen und peripheren Nervensystem nach den neues
ten Forschungen. Centralbl. f. allg. Path. u. path. Anat., Bd. 6, p.
849.
Tello, F. Cited after Cajal.
Tuckett, J. L. 1896 On the structure and degeneration of non-medullated
nerve fibers. J. of Phys. Camb., vol. 19, p. 267.
Van Gehuchten, A. 1904 Cited after Cajal.
Waller, A. 1852 Cited after Cajal.
WiETiNG, J. 1898 Zur Frage der Regeneration der peripherischen Nerven.
Beitr. z. path. Anat. u. z. allg. Path., Bd. 23, p. 42.
Wilson, J. G. 1909 The present position of the theory of autoregeneration of
nerves. Anat. Rec, vol. 3, p. 27.
ZiEGLEU, P. 1896 Untersuchungen iiber die Regeneration des Achsencylinders
durchtrennter peripherer Nerven. Arch. f. Klin. Chirurgie, Bd. 51,
p. 796.
PLATE 1
EXPLANATION OF FIGURES
The drawings were made from pyridine-silver preparations of the degenerating and regenerating sciatic nerve of the adult dog.
1 Ocu. 3, Obj. 2 mm. Degenerating medullated axon in the distal stump
on the secdnd day.
2 Ocu. 3, Obj. 2 mm. Two medullated fibers from the distal stump on the
fourth day. Degeneration has progressed much farther in a, than in b. The
neurilemma can be seen bounding the unstained myelin sheath.
3 Ocu. 3, Obj. 2 mm. Medullated fiber from the distal stump on the eighth
day; a, fragmented axon surrounded by an elliptical segment of myelin.
4 Ocu. 3, Obj. 2 mm. Early protoplasmic band formed from a medullated
fiber. From the distal stump on the nineteenth day; a, nucleus; b, droplet of
myelin containing fragments of axon.
5 Ocu. 3, Obj. 2 mm. A bundle of degenerating non-medullated fibers from
the distal stump on the second day.
6 Ocu. 3, Obj. 2 mm. Undegenerated non-medullated fiber from the distal
stump on the fourteenth day.
7 Ocu. 3, Obj. 2 mm. Three protoplasmic bands formed from non-medullated fibers. From the distal stump on the nineteenth day.
8 Ocu. 3, Obj. 2 mm. Non-medullated fiber from the neighborhood of the
cut surface of the distal stump, showing new formed lateral branch with endbulb. End of first day; c, toward the center; p, toward- the periphery.
9 Ocu. 3, Obj. 2 mm. Non-medullated fiber from the neighborhood of the
■cut surface of the distal stump, showing branching and two end-bulbs. End
of first day; c, toward the center; p, toward the periphery.
10 Ocu. 3, Obj. 7. Medullated fiber from the neighborhood of the cut surface of the distal stump on the third day; a, disintegrated portion of the axon;
b, club-shaped extremity of the living part of the axon; d, isolated neurofibril;
c, toward the center; p, toward the periphery.
11 Ocu. 3, Obj. 2 mm. Medullated fiber from the neighborhood of the cut
surface of the distal stump on the third day, showing fibrillar reticulum, isolated fibrils, and one fibrillar side branch with bulb; c, c', toward the center; p,
toward the periphery.
12 Ocu. 3, Obj. 2 mm. Formation of side branches and end-bulbs on the
non-medullated fibers near the cut surface of the proximal stump at the end of
the first day.
538
DEGENERATION AND REGENERATION OF NERVE FIBERS
S. WALTER RANSON
PLATE 1
P
d — .
10
539
Pl.AT]-: 2
EXPLANATION OF FIGUUES
13 ()cu. o, ()!)]. 7. Humlk' of regenerating non-niedullated fibers in the
|)r()xiinal stump, on the fourteenth day; c, toward the center; p, toward tlie
j)erii)liery.
14 Ocu. 3, Obj. 2 mm. JNIediiUated fiber from the neighborhood of the cut
.surfac(> of the proximal stump at the end of the first day; a, degenerated portion
of the fiber; b, zone of reaction with neuro-fibriUar reticulum; d, only slightly
altered portion of the axon; c, toward the center; p, toward the periphery.
15 Ocu. 3, Obj. 2 mm. Fibrillar dissociation in a meduUated axon in the
neighborhood of the cut surface of the proximal stump on the second day.
16 Ocu. 3, Obj. 2 mm. Two medullated axons, which have grown out from
the cut surface of the proximal stump and given off fine branches in the exudate;
c, c', toward the center; p, p', toward the periphery.
17 Ocu. 4, Obj. 2 mm. Medullated axon from the neighborhood of the cut
surface of the proximal stump at the end of the first day. Many fine branches
arise from its surface and end in small bulbs.
18 Ocu. 4, Obj. 2 mm. From the neighborhood of the cut surface of the
proximal stump on the fourth day ; c, obliquely cut medullated fiber with a tubular
plexus of fine branches beneath the neurilemma; b, another tubular plexus
derived from a medullated axon; c, row of degenerating non-meduUated fibers
and their end-bulbs.
19 Ocu. 3, Obj. 7. Plexus derived from a medullated axon. From near
the cut surface of t he proximal stump on t he second day.
.540
DEGENERATION AND REGENERATION OF NERVE FIBERS
S. WALTER HANSON
P
PLATE 2
14
541
PLATE 3
EXPLANATION OF FIGURES
•_' ) Ocii. o, (>l).j. 7. Branching of a modullatod axon. From a point several
milliinclcrs al^jve the cut surface of the proximal stump on the nineteenth day;
(I, ])oint in old axon from which arises an extremely short branch wliich at once
divides into two; c, toward the center; p, toward the jieripher}'.
21 Ocu. 3, Obj. 7. Branches of a medullated axon of the proximal stumi)
several millimeters above the cut surface on the twenty-fifth day; c, toward the
centei'; />, toward the jjeriphery.
22 Ocu. 3, Obj. 7. A branch on the side of a non-medullated fiber which
might itself however be a branch of a medullated axon. From the proximal
stump on tlie fourteenth day.
2o Ocu. 3, Obj. 7. Bundles of new axons in the i)roximal stuni]) on the tliirt}'foiirl h day.
24 Ocu. .">, Obj. 7. .\ bundle and a tangled skein of new axons from the
central stump on llie 1 liirly-fourf li da_\'; r. tdward tli(> center; [>, lowai'd tli(>
IK'riphery.
2.T Ocu. 3. Obj. 7. A cross section of three bundles and one tangled skein
of new axons, from t lie cent r;il st ump 1 liii'ty-four d;iys after the operation.
542
DEGENERATION AND REGENERATION OF NERVE FIBERS
S. WALTER RANSON
D P
\ Aiu.'ii
20
22
PLATE 3
P
24
25
543
PLATE 4
EXPLANATION OF FIGTtRES
2C) Ocu. 3. Olij. 2 mm. Fiom a cross section of the proximal stump on the
thirty-fouith day showing the increase in the number of non-meduUated fibers;
II. l)iuidk" of non-medullated fibers; b, medullated fiber.
27 Ocu. 3, Obj. 2 mm. Bundles of new axons in the scar on the twenty-fifth
day; a branching fibers; c, toward the center; p, toward the periphery.
28 Ocu. 3. Obj. 7. Five protophismic bands, down one of which a new axon
is growing. From tlie distal stump thirty-four days after the operation; c,
toward the center; p, toward the periphery.
29 Ocu. 3, Obj. 2. mm. Cross section of the distal stump on the thirty-fourtli
day; a, protoplasmic band from a medullated fiber containing five new axons;
f>, bundles of protoplasmic bands from non-medullated fibers some of which contain new axons; r, di'oplct of meylin in a protoplasmic band.
544
DEGENERATION AND REGENERATION OF NERVE FIBERS
S. WALTER HANSON
PLATE 4
T
O
26
28
545
THE CESSATION OF MITOSIS IN THE CENTRAL
NERVOUS SYSTEM OF THE ALBINO RAT
EZRA ALLEN
From the Philadelphia School of Pedagogy and The Wistar Institute of Anatomy and
Biology
TWENTY-TWO FIGURES
• INTRODUCTION
While different observers have recorded the fact that mitosis
continues in the central nervous system after birth in mammals
which are relatively immature when born, the exact period of
its cessation in any one such animal does not seem to have been
determined. The purpose of this paper is to record results of
studies which I have been pursuing, with many interruptions,
for three years, in the effort to discover how long cell division
may continue after birth in the central nervous system of the
albino rat.
The literature on this phase of vertebrate growth is not extensive. Buchholtz ('90) records mitoses in all parts of the central
nervous system of new-born dogs and rabbits and those a few
days old. Sclavunos ('99) states that in new-born dogs, cats
and white mice dividing cells are to be found in the wall of the
central canal of the cord, in its white substance, in the substantia gelatinosa, in the anterior gray horns, at the point of
entrance of the dorsal and ventral nerve roots, "among the cells
of the spinal ganglia," in the , dorsal and ventral septa of the
Cord, in the dura, and abundantly" in the arachnoid and under
the pia. Hamilton ('01) found mitoses in the cerebrum and spinal
cord of the albino rat in animals four days old. Addison ('11),
in his study of the Purkinje cells of the same animal, notes mitoses
regularly occurring in the cerebellar cortex at twenty-one days,
and in one individual at twenty-two daj's after birth.
547
548 EZRA ALLEN
MATERIAL AND TECHNIQUE
I am indebted to The Wistar Institute of Anatomy and Biology
for the albino rats used in the study and for the use of its laboratory equipment. I am indebted to Dr. Stotsenburg, of the Institute, for a supply of rats as needed and for courteous attention;
to Dr. H. D. King for a method of imbedding and staining; to
Dr. S. Hatai for valuable suggestions. To Dr. H. H. Donaldson
I am especially indebted for constant aid and criticism.
My method of work was in general as follows. Healthy rats
of the following ages were used: 1, 4, 6, 7, 12, 15, 18, 20, 30, 52, 70,
about 120 days old, and one about two years old. In all, some
twenty-five different animals were studied. Record was made of
the weight, body-length and sex. After chloroforming the animal,
the brain and cord were quickly removed, fixed in Carnoy's fluid
and imbedded, the younger specimens in paraffin the older in
celloidin and paraffin. Frontal sections were then cut at 8 micra
and stained with either iron-alum-haematoxylin or thionin, followed by eosin or erythrosin. Thionin was found to differentiate
the mitotic figures with sufficient clearness for this' study. By
using the mechanical stage, the sections were thoroughly explored
with a magnification sufficient to detect mitoses. Only those
cells which showed mitotic figures clearly were enumerated; the
earlier stages of prophase, being more difficult to identify, were
not considered. The Zeiss 4 mm. objective and No. 4 eyepiece usually sufficed; in doubtful cases the 2 mm. oil immersion
objective and eye-pieces higher than No. 4 were employed.
Two methods of record were used. With the younger material,
diagrams representing the sections studied were outlined and on
these the approximate location of the dividing cells was indicated,
the number 1 being employed for the cells in section No. 1, the
number 2 for those in section No. 2, etc. (figs. 1 to 4). When
the examination of a series was complete, this method showed
graphically the distribution of the dividing cells in that portion'
of tissue both in cross section and longitudinally. The other
method, usually employed for the older material, was to tally the
cells as discovered opposite the number of the section, regional
location being indicated by columns if desired.
MITOSIS IN CENTRAL NERVOUS SYSTEM
549
All the figures are from frontal sections of the cord and brain of the albino rat.
Figs. 1 to 4 Diagrammatic drawings of frontal sections through the cervical
cord and at three different levels of the cerebrum of a one-day-old rat. Each
figure shows the position of a dividing cell in the section of the series corresponding
to that number. The dotted lines outline gray matter. The ventral portion of
the tissue appears at the bottom.
/ ,'
\ \
I \
/ I
- I
/ /
10 ^
Fig. 1 Distribution of the dividing cells in ten consecutive sections of the cervical cord at the level of its greatest area. X 75.
As to the portions of the central nervous system studied. At
first examination was made at various levels throughout the length
of the cord, cerebellum and cerebrum to determine whether mitosis was limited to a particular locality. Then, in order to determine numerical relationships, attention was focussed upon certain definite levels. For the spinal cord, the sections showing
greatest area in the cervical, thoracic and lumbar levels; for the
cerebellum, sections passing through the region showing greatest
area, and for the cerebrum sections passing through the optic
chiasma were chosen. In each instance frontal sections were
used. The number of sections thus studied varied a little —
in the cord at least ten and frequently more: in the brain at
least five and frequently more.
3
550
MITOSIS IN CENTRAL NERVOUS SYSTEM
551
Fig. 2 Distribution of the dividing cells in five consecutive sections cut through
the frontal lobe of the cerebrum dorsal to the olfactory lobe. X 25.
Fig. 3 Distribution of the dividing cells in five consecutive sections cut through
the optic chiasma. X 25.
Fig. 4 Distribution of dividing cells in five consecutive sections cut through
the mid-brain and the occipital lobes of the cerebrum posterior to the lateral
ventricles. X 25.
THE JOUHNAL OF COMPARATIVE NEUROLOOY, VOL. 22, NO. 6
552 EZRA ALLEN
As a basis for determining the comparative rate of cell division the number of mitoses per cubic millimeter was obtained.
With the aid of the camera lucida or projection apparatus, drawings were made of the first and last sections of a series. These
drawings were then measured by the planimeter and the mean
area taken. Since the sections were of a fixed thickness (8 micra)
the volume of the tissue in question was readily calculated. The
number of dividing cells in the series of sections had already been
determined, so that the necessary data for finding the number of
dividing cells per cubic millimeter of tissue were at hand.
STATEMENT OF RESULTS
The distribution of mitoses
A brief statement will first be made under this head to be followed by more detailed explanation. The results of this study
show that at birth mitoses are occurring in each division of the
central nervous system, at all levels of the cord, cerebellum and
cerebrum. An examination of figures 1 to 4 will make it evident
that the general distribution, however, is unequal. Table 2
(p. 557) indicates at different ages the relative mitotic activity
per cubic millimeter at the three principal levels of the cord and
at one level of the cerebellum and cerebrum respectively. Figures
2 to 4 show the relative longitudinal distribution at three levels
in the cerebrum, as well as the fact that in this organ the region
of greatest activity is in the walls of the lateral ventricles. In
the cerebellum dividing cells are most abundant in the cortex.
Table 2 shows the relative rate of mitosis at different levels for
the ages from one day to twenty-five days after birth. This
table shows also that cell division stops earliest in the cord, a
little later in the cerebellum and still later in the cerebrum.
With these data in mind we may pass to the details.
1. The distribution as it appears in frontal section will bo better
appreciated by a preliminary consideration of the embryonic
differentiations of tissue as they appear in the central nervous
system. The original epiblastic layer forming the wall of the
neural tube is early converted into a protoplasmic framework
MITOSIS IN CENTRAL NERVOUS SYSTEM
553
(myelospongium) which has a columnar and radial disposition
and shows three layers: (a) the innermost or germinal zone;
(b) a middle nuclear or mantle zone crowded with daughter cells
which have migrated from the actively mitotic germinal layer;
and (c) an outer nuclear-free reticular or boundary zone. (His
'89 and '04; Hardesty '04; Bryce '08). The seat of mitotic
activity is confined at first to the germinal zone but later spreads
to the mantle layer (Hamilton '01; Hardesty '04). Activity
continues in these two layers with increasing age, but becomes
more rapid in the latter (the middle nuclear or mantle) . Hamilton ('01), writing of the spinal cord of the albino rat, states: "As
TABLE 1
Giving the percentage of ependynial mitoses in the spinal*cord of the albino rat from
one day to fifteen days old, based upon the number of mitoses in ten sections from
the cervical, thoracic and lumbar levels respectively, excepting that in the fifteenday rat twenty sections at each level were used.
AGE
TOTAL NUMBER OF MITOSES
EPENDTMAL MITOSES
PBKCENTAGE OF
EPENDYMAL MITOSES
days
1
4
6
12
15
47
96
115
22
4
4
6
2
1
8.5
0.0
5.2
9.0
25.0
Totals
284
13
4.5
The percentage of 13 to 284 is 4.5, the percentage of the ependymal mitoses to
the total number of mitoses during the period from 1 day to 15 days.
development proceeds, there is a relative increase of extra-ventricular mitoses, so that by th^ end of the first day after birth
they are greatly in the majority." My preparations from the
one-day cord of the same animal confirm this observation. At
this age the mitoses are distributed in the ependyma, in the white
and gray regions, in the fiber tracts, in the nerve roots, in the
enveloping membranes and among the spinal ganglion cells.
"With advancing age the distribution appears as shown in table 1,
the data for which were obtained by adding together the number
of mitoses found in ten sections taken from the cervical, thoracic
554 EZRA ALLEN
and lumbar regions of the cord respectively, with one exception,
viz., that twenty sections instead of ten were used from each
region as a basis for the figures for the fifteen-day specimen.
Hamilton ('01), from observations on twenty-five consecutive
sections from the lumbar cord of one new-born rat, concludes
that the greatest number of mitoses is in the anterior gray column.
This relationship apparently does not persist during the later
stages of mitotic activity, as shown by my sections. Furthermore the animals which I have studied show great individual
variation at the same age. In addition, the same animal varies
greatly in its number of mitoses in series of sections taken at only
short distances apart in the same approximate level.
The ependyma of the cerebellum shows very few mitoses in the
one-day-old animal. ' In the cortex they are abundant; there are
few in the intermediate tissue. This condition prevails throughout the length of the organ. By the age of twelve days cell
division is confined to the cortical area and does not reappear in
other portions.
The cerebrum shows a distribution the reverse of that found
in the other two divisions. While at birth it is diffuse, the greatest amount of activity is seen in the germinal and mantle layers
about the lateral ventricles (fig. 3). The activity external to
these layers grows less until at the age of twelve days there is
scarcely any cell division elsewhere. Furthermore, the activity
about the lateral ventricles is not equally distributed. It is least
on the ental lateral surface and the ventral portion of the ectal
wall; greatest along the roof and dorsal portion of the ectal lateral
wall, where the mantle layer is widest (fig. 7) . This distribution is
to be seen in the animal one day old at whatever level of the ventricle we may section. In the older animals the region of activity
becomes limited to the small portion of the ectal lateral wall lying
a little ventrad from the point of union of this wall and the roof.
(See further discussion of this zone under the topic Structural
Correlations).
2. A comparison of sections from the same rat taken at different levels shows that the rate of mitosis is not equal throughout
the length of the central nervous system. The cord is the region
MITOSIS IN CENTRAL NERVOUS SYSTEM 555
of the least and the cerebellum the seat of the greatest activity,
while the cerebrum in that portion where cell division is most
rapid exhibits an activity somewhat greater than that of the cord.
Table 2 (p. 557) contains figures illustrating these different rates.
In addition, mitotic activity is unequal at different levels of the
cord and cerebrum. Table 2 brings out this relativity for the
cord. The rate of cell division is seen to be lowest in the thoracic
and highest on the whole in the cervical portion. In the latter
it rises on the sixth day to a rate equal to the most rapid exhibited
by the cerebrum (on the fourth day), and more than twice as
rapid as that of the cerebrum at six days. From a comparison
of numbers of dividing cells at the three levels of the cerebrum,
it is found that the greatest number is in the region of sections
which pass through the optic chiasma.
This unequal longitudinal distribution is still further illustrated
in a small way within the limits of each level, as shown by the
markedly greater number of mitoses to be found in two or more
consecutive sections of a series, this greater number standing out
prominently from the relatively smaller number in the sections
immediately preceding and following. Three illustrations follow, chosen from many which show the same relationship. The
figures representing the number of mitotic cells in each section of
the series run as follows: (1) from the cerebrum — 4, 5, 7, 9, 11, 16,
14, 21, 3, 9, 3, 9, 3, 4; and (2) from the cervical cord 4, 0, 2,
3, 5, 8, 1, 4, 2. The numbers itaUcized in each series mark
this grouping of mitotic activity, which may be termed a 'locus'
of activity. Similar loci. appear in the cerebellum. (3) A brilliant illustration presented itself in the cerebrum of a twentyfive-day specimen, an age when the mantle layer is not so crowded
with nuclei as it is in younger material. This illustration will
also show the tendency of cells to form groups and to retain a
group identity. In this instance three well-marked groups of
closely-packed, densely-staining nuclei were found, each well
differentiated from the surrounding nuclei, and each showing
mitoses. (See mn^-^mn^ in fig. 10; enlarged view of one group is
to be seen in fig. 21). These groups extended through three consecutive sections of 8 micra. I have not endeavored to ascertain
556 EZRA ALLEN
whether such loci are constant in their appearance at fixed points
of the system or vary with different individuals. The large number of such loci found within small portions of the tissue at all
ages and in each individual examined shows the necessity of using
a considerable number of consecutive sections if one desires to
make wide application of figures obtained from any one level.
3. Mitosis continues for different periods after birth in the
different levels. It ceases first in the cord. Very few dividing
cells are to be found in the fifteen-day cord at any level, as shown
in table 1 (p. 553). No dividing cells were found in two eighteenday-old specimens, although sections widely distributed in the
different levels respectively were examined. No mitoses were
found in the cords of older animals. The eighteen-day period
may then be regarded as the time when mitosis has ceased in
this portion of the system, having ceased between this and the
fifteen-day period.
In the cerebellum it continues until some time between the
twenty-second and twenty-fifth day, while in the cerebrum it
continues still longer — to a slight degree in material about 120
days old, further discussion of which is taken up under the topics
which follow.
4. Table 2 shows the distribution of dividing cells per cubic
millimeter at tliree levels in the spinal cord and at one in the cerebellum and cerebrum respectively. The data for these figures
come from consecutive frontal sections at the different levels as
fully described in the introduction (p. 552). Each number in
the table is not an average from several different rats but is taken
from the records of one individual. For a given age, the numbers
italicized are from the same animal. It will be noticed that the
figures for the cerebellum in each of the animals of the first three
ages are not from the same, animals as those which furnished the
figures for the other levels. This substitution is due to certain
technical difficulties which presented themselves, such as failure
to get good sections or to obtain true frontal sections in the
desired locality. These three cerebella arc the only ones of these
ages upon which estimations were figured; others might have
furnished slightly different figures.
MITOSIS IN CENTRAL NERVOUS SYSTEM
557
TABLE 2
Showing the number of mitoses -per cubic millimeter of nerve tissue in the central
nervous system at certain levels. The figures are taken from calculations of the
volume of tissue and the number of mitoses in ten consecutive sections at each level of
the cord, five in the largest portion of the cerebellum and five in the cerebrum in the
region of the optic chiasma {see p. 552) . The numbers italicized are from the same individual of that age. Theletters (a), (6) and (c) refer to different rats of the same age.
CORD
CEREBELLUM
Cervical
Thoiacic
Lumbar
days
1
208
115
259
1597
430
4
6
12
437
46
176
236
75
351
320
U
2111
(7-day)4848
839
U7
193
37
20
00
00
00
(a) 00
(a) 18
20
00
00
00
(b) 61
(b) 27
20
00
00
00
(c) 520
25
00
00
00
00
27
The differences of quantitative distribution which appear from
this table if one reads the figures from left to right (according to the same age) have been noted on page 555. If one reads
the columns downwards, it appears that the rate of cell division
increases after birth (a confirmation of Hamilton '01) until the
sixth day in the cord and the seventh in the cerebellum, but in the
cerebrum only until the fourth day; after these respective dates
the rate decreases rapidly. Cell division has ceased in the cord
at the twentieth day, in the cerebellum at the twenty-fifth day,
but in the cerebrum is still continuing at this last age at the same
rate as for the twentieth day in specimen b.
Since these figures are taken from so limited a number of
animals, of each age, and from a length of only 80 micra in the
cord and 40 micra in the brain at each level, they are to be interpreted as representing the general movement of mitotic activity,
not as furnishing the basis for an accurate curve which will show
the rate of mitosis after birth. More data must be gathered
before such a curve can be constructed. However, the wide
difference at each age between the rate in the cerebellum and the
other levels indicates that we are safe in concluding that this
organ presents the greatest degree of activity. There is good
558 . EZRA ALLEN
reason for this condition since at birth the cerebellum is developed to only a sUght degree, and its growth thereafter is very
rapid during its first twenty-five days of Ufe.
Hamilton ('01) found that the rate of cell division is less at
birth than before birth. Unfortunately her paper does not give
the embrj^onic age at which the rate is highest. Otherwise we
might fix approximately the two periods in the hfe history of the
albino rat when this factor of growth is most important in the
cord and cerebrum. Since the figures given by her are not in
terms of number per cubic millimeter, we have not the data
needed for an exact comparison of the two phases of growth.
STRUCTURAL CORRELATIONS
1. Correlations in the spinal cord
If we compare sections of the cervical cord from one-day and
twenty-day rats respectively, we see several morphological differences (figs. 5 and 6). (1) In the first place, the wall about the
central canal of the one-day animal shows germinal cells in mitosis, and shows also that its myelospongium at each end lacks
nuclei. Neither of these phenomena appears in the older material.
In addition, the form of the canal in the older differs from that
of the younger in that it approaches more nearly the strongly
elongated oval assumed in the adult cord. (2) The number of
cells in the immediate vicinity of the canal of the twenty-day
animal is less than in the one-day old. (3) There is greater
degree of maturity in all the cells of the older as indicated by
their size and cytoplasmic development. And (4) the number
of migrating cells is much less in the older than in the younger animal, although the region of greatest migrating activity remains
the same in both ages — the region just ventral to the canal.
In most vertebrates the germinal and mantle layers about the
canal have been completed some time before birth. One known
exception is the chick. Merk ('86) figures the cord of a chick
of seven days and five hours old which shows a nuclear-free
space in the germinal zone at each end of the canal, a condition
found in the albino rat at six days.
^■■'f
Figs. 5 to 11 Untouched photographs of frontal sections through the cord and
cerebrum of albino rats of different ages. They show the ventral side downward
on the page. The letters indicate the same structures throughout: ventr, ventral;
eci, ectal; enl, ental; r, roof; V.iii, third ventricle.
Fig. 5 One-day rat, cervical cord . X 84.
Fig. 6 Twenty-day rat, cervical cord. X 84.
559
560 EZRA ALLEN
The germinal layer is completed progressively in the different
levels of the cord in the albino rat. The completion is earliest
in the thoracic region, where it is fully formed by the twentyday period. It matures next in the lumbar region, where the
wall is closed in nearly every section of the twenty-five-day and
in everj^ section of the thirty-day-old animals. In the cervical
region, finally, a few sections at the last-named age still show
a nuclear-free myelospongium at the ventral portion. The
dorsal end is closed at all levels in the interval between the sixday and twelve-day periods.
2. Correlations in the cerebellum
The most interesting feature here is the external granule
layer. Mitosis continues in this layer after it has ceased in all
other parts of this organ. It ceases when the inward migration
of the nuclei has taken place, a movement which is usually completed between the twentieth and twenty-fifth day (Addison
'11). I found that in one specimen examined the migration had
been completed at twenty days. Addison ('11) found in one of
his preparations dividing cells in this layer at twenty-two days.
Examination of two twenty-five-day specimens prepared by me
revealed no mitoses; neither was any trace of the external granule layer present.
3. Correlations in the cerehrum
The well develo])ed and persistent mantle zone lying along the
ectal wall of the lateral ventricles is of particular interest, for in
it occur the dividing cells found in the oldest specimens which
show mitoses, and this layer, unlike the external granule layer of
the cerebellum, never entirely disappears in animals up to two
years of age, the oldest which I have examined (fig. 9). The
one-day and twenty-five-day specimens })oth show dividing cells
at every level along the entire length of the ventricles. In each
case they are most abundant at the level of the optic chiasma.
The mantle zone, while in general following the outline of the
ventricular wall, is not of the same thickness throughout in any
MITOSIS IN CENTRAL NERVOUS SYSTEM
561
X
E X
2 X 's "
bio '^ bhi th
s i s s
562
EZRA ALLEN
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if
■^
-/3
o
— ^
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c
r.
O
3
o
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o g
c ^ SO
'^ ^ X
i ,1 ' •
^
..•<
1
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1
^ S 3
bO
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_- _^ f.
^ Oi a:
— — :2
^ o ~
„ GO o
2 .^x
3
c ^
MITOSIS IN CENTRAL NERVOUS SYSTEM 563
frontal section (figs. 7 to 11). It is widest at the point where the
ectal lateral wall and the roof meet, and wider all along the ectal
lateral wall than along the ental wall. In the one-day animal the
layer extends all around the ventricle, but, beginning at the ventral portion, it is gradually reduced in extent until at twentyfive days old it consists of a single layer on the ental lateral wall ;
on the roof it is in almost the same condition, while on the dorsal
portion of the ectal lateral wall and extending well outward at
the point it is still several cells in thickness (fig. 10). Reduction
is nearly complete along the ental lateral wall at the six-day period
(fig. 8). In the twenty-five-day specimens cell division is occurring only in the portion of the ectal lateral wall and roof betw^een mn^ and mn^ in figure 10. In this region a total of eight
dividing cells was found in a seventy-day animal in five frontal
sections at the level of the optic chiasma, these being along the
ectal lateral wall, with none on the roof.
The mantle layer persists in this limited region along the ectal
lateral wall in the two-year animal, as shown in figures 9 and 11.
The active portion of this layer continues in advanced age to
occupy the region a few cells in width external to the germinal
layer, as shown by figures 21 and 22. There is evidently some
connection between this layer and the "Uebergangsschichten'^
of His ('04) shown in his section of the human foetal cerebrum
of four months.
NATURE OF THE DIVIDING CELLS
The tissues ultimately found in the nervous system are the
neurones, the neuroglia and the connective tissue. In addition
we find occasional leucocytes and a relatively greater number of
lymphocytes. Hardesty ('04) from his study of the developing
neurogha of the pig, concludes that, With the present technique there is nothing to show that all the products of the mitoses
(germinal cells) in the ependjrmal layer are not indifferent elements from the first — capable of developing into either neurones
or neuroglia." The neurogha tissue has a double source of origin,
arising from both the ectoblast and mesoblast. Hatai ('02) con
\ 1 eu
Figs. 12 to 22 Camera lucida drawings of i)ortions of tissue in cord and cerebrum chosen to show dividing cells. All the drawings were made with the Zeiss
2 mm. oil immersion lens and No. 6 eye-piece, tube length 176 mm. The drawings
have been uniformly reduced to make the magnification as printed equal 800 diameters. The letters indicate the same structures throughout: tnli, membrana
limitans interna; g, dividing cell in germinal layer; mn, dividing cell in mantle
(middle nuclear) layer; ep, ependymal cells; dt, cells in differentiated tis.sue; leu,
leucocytes; ca, cell of capillary wall.
Fig. 12 Four-day rat, cervical cord; dividing cell in germinal layer. X 800.
Fig. 13 Six-day thoracic cord; large dividing cell in posterior horn. This cell
is one of two dividing cells very near each other, each of which showed its chomosomes in three con.secutive sections of 8 micra each. X 800.
Fig. 14 Twelve-day thoracic cord; small dividing cell in posterior horn. X 800.
Fig. 15 Twelve-day thoracic cord; mesodermal dividing cell of capillary found
in postero-lateral tract; same section as figure 14. X 800.
Fig. 16 Six-day cerebrum, cortex; leucocyte within a cross section of capillary
and a dividing cell. It is difficult to determine whether the granular mass about
the nucleus of the leucocyte is its cytoplasm or other material. X 800.
564
m
m
(r - g
■OQ.
^ m n
Figures 17 to 22 are from the cerebrum of rats of different ages, showing portions of the zones bordering the ectal lateral wall of the lateral ventricle at about
the locality marked mn^ in figure 10, with the exception of figure 19, which is from
the cortex.
Figs. 17 and 18 One-day cerebrum; small portions of germinal layer separated
from each other by only a few cells. X 800.
Fig. 19 One-day cerebrum; small portion of the cortical region of the same
section as figures 17 and 18. X 800.
Fig. 20 Six-day cerebrum; adjacent portions of germinal and mantle layers.
X 800.
Fig. 21 Twenty-five-day cerebrum; two dividing cells in mantle layer, the
lower at the edge of a group of cells {inn^ in fig. 10). (See p. 555.) X 800.
Fig. 22 120-day cerebrum; germinal and mantle layers and two cells showing
cytoplasm in the first layer of differentiated tissue. At this age the ependymal
cells are clearly differentiated; they began to appear in the twenty-five-day
material, as shown in figure 21. The reduction in the number of cells in the two
inner layers is to be noticed. X 800.
565
566 EZRA ALLEN
firms the observations of Fragnito and Capobianco with regard
to the mesoblastic source:
From these observations the conclusion is drawn that the neurogUa
nuclei in the white rat as well as in the mouse represent two distinctly
characterized types: namely, nuclei the structure of which resembles
very closely that of the nerve cells, and the nuclei the structure of which
resembles very closely that of endothelial cells which form the capillary
wall. These two types of nuclei have been derived from the ectoblast
and mesoblast respectively. The latter type has probably two sources
of origin; that is, they are partly derived from mesoblastic cells immigrating from the meninges (Capobianco and Fragnito), and partly from
proliferating endothelial cells of the walls of the capillaries, these cells
having separated from the capillary wall and migrated into the surrounding tissue, where they constitute one type of the neuroglia elements.
Hamilton (^01) differentiates two types of dividing cells in the
cerebrum and spinal cord, the one, large with cytoplasm well
developed and the chromosomes more scattered, the other small
without cytoplasm and with the chromosomes solidly bunched.
The former, she thinks, develop into nerve cells and the latter
into neuroglia. Hardesty ('04) is of the opinion that the neuroglia
cells cannot be differentiated from the inward-migrating white
fibrous corpuscles. My observations lead me to agree with
Hardesty, and so far as my methods of staining reveal any differentiations there seems to be no way of determining whether the
small dividing cells are to become neurones, neuroglia cells or
white fibrous corpuscles, since the small neurones which show
processes very plainly are no larger than some of the dividing
cells (figs. 14 and 16).
My preparations indicate that division in the two sizes of
mitotic cells does not continue to the same period in the cord and
cerebrum. In the cord, the large cells are found dividing in
various regions up to the sixth day (fig. 13). While twelve-day
specimens still show some mitoses in the germinal zone, the dividing cells of the extra-opcndymal regions possess the characteristics of the smaller type. In the cerebrum the chromatic mass in
the dividing cell measures up to 7.5 x 8 micra in the younger
material, while in 7()-day and 120-day material, a list of measurements runs as follows, the tissue from the two animals having
MITOSIS IN CENTRAL NERVOUS SYSTEM 567
been prepared in the same manner: 70-day — 5 x4, 5.5 x 5, 6x4,
6x3 micra; 120 day — 6 x 4, 4 x 5, 4 x 4 micra. None were found
measuring more than 6x4 micra.
The dividing cells which I have enumerated in this study are
believed not to be leucocytes or lymphocytes for the following
reasons : the size of the nuclei in leucocytes found in blood vessels
in my preparations is from. 3.2 x 3.2 micra to 3.8 x 3.8 micra,
while the chromatin material in the nerve nuclei measures from
4 X 4.2 in anaphase to 7.5 x 8 micra in prophase and metaphase.
Moreover, after the dividing cells have disappeared from all other
areas they are still to be found in the limited zone along the lateral ventricles of the cerebrum which has already been described.
They are to be found also in the neighborhood of capillaries but
this association is not constant.
The differentiation from lymphocytes is easier. These are
found scattered through the tissue; they are smaller than the
leucocytes and are readily recognized by the characteristic nuclei,
their chromatin being gathered into one, two or more well separated, densely stained spherical masses, the outlines of which are
always smooth and regular, lying in a clear nuclear matrix
bounded by a limiting membrane of uniform thickness.
4
CONCLUSIONS
1, Mitosis ceases in the central nervous system of the albino
rat as follows: (a) No mitoses are found in the cord at any level
after the eighteenth day. This is somewhat previous to the
complete cellular differentiation of the wall of the central canal,
a stage accomplished in the thoracic region by the twentieth day
after birth, in the lumbar region by the thirtieth day after birth,
while at this last-named age the cervical level shows in occasio^ial
sections a portion of the wall still incomplete, (b) In the cerebellum mitosis ceases when the migration of the cells in the external
granule layer is complete, a condition reached between the twentieth and twenty-fifth day after birth, (c) In the cerebrum mitosis
continues with a considerable degree of activity to the twentieth
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL, 22. NO. 6
568 EZRA ALLEN
day after birth, after which it is found to a sUght degree in the
mantle layer along the ectal lateral wall of the lateral ventricles,
this layer persisting at least to the age of two years. The latest observation of dividing cells in this locality was in 120-day
material.
2. The rate of mitosis increases for a time after birth, reaching
its high point at about the seventh day for the cord and cerebellum and about the fourth day for the cerebrum.
BIBLIOGRAPHY
Bryce, T. H. 1908 Quain, Elements of Anatomj^* vol. 1.
BucHHOLTz, A. 1890 Ueber das Vorkommen von Karyokinesen in Zellen des
Centralnervensystems von neugeborenen und jungen Hunden u. Kaninchen. Neur. centralblatt, Bd. 9, pp. 140-143.
Hamilton, Alice 1901 The division of differentiated cells in the central nervous system of the white rat. Jour. Comp. Neur., vol. 11, pp. 297-320.
Hardestv, I. 1904 The development and nature of the neuroglia. Am. Jour.
Anat., vol. 3, pp. 229-268.
Hatai, S. 1902 On the origin of neuroglia tissue from the mesoblast. Jour.
Comp. Neur., vol. 12, pp. 291-296.
His, W. 1886 Zur Geschichte des menschlichei^ Riickenmarks u. d. Nervenwurzeln. Des XIII Bandes d. Abhandl. d. math.-phys. Klasse d.
konigl. Sachsischen Gesellschaft d. Wissenschaften No. VI.
"" 1889 Die Neuroblasten und deren Entstehung im embryonalen Mark.
Arch, fiir Anat. u. Entwick.
' 1904 Die Entvvickelung d. menschlichen Gehirns wiihrend d. ersten
Monate. Leipzig.
Merk, L. 1886 Die Mitosen im Ccntralnervensystem. Denkschr. d. math,
naturw. Klasse d. kaiserl. Akad. Wiss., Bd. 53, Wien.
ScLAVUNOS, G. 1899 Ueber Keimzellen in d. weisscn Substanz d. Ruckenmarks von alteren Embryoncn und Neugeborenen. Anat. Anzeiger,
Bd. 16, pp. 467-473.
SUBJECT AND AUTHOR INDEX
D
AGE, sex, weight and relationship upon the
number of niedullated nerve fibers and on
the size of the largest fibers In the ventral
root of the second cervical nerve of the albino
rat. The influence of 131
Allen, Ezra. The cessation of mitosis in the
central nervous system of the albino rat. 547
CARPENTER, F. VV. On the histology of the
cranial autonomic ganglia of the sheep. 447
Cauda equinas or the sciatic nerves. Experimental studies of paralyses in dogs after mechanical lesions in their spinal cords, with a note
on 'fusion' attempted in the 99
Centers in teleosts. The olfactory tracts and 177
Cerebral ganglia. The epibranchial placodes of
Lepidosteus osseus and their relation to the 1
nerve of the albino rat. The influence of
age, sex, weight and relationship upon the
number of niedullated nerve fibers and on the
size of the largest fibers in the ventral root of
the second 1.31
Cranial capacity. A comparison of the European
Norway and albino rats (Mtis norvegicus and
Mus norvegicus albinus) with those of North
America with respect to the weight of the central nervous system and to 71
Cyclostomes. The telencephalon in 341
EGENERATION and regeneration of nerve
fibers 487
Dogs after mechanical lesions in their spinal cords,
with a note on ' fusion' attempted in the cauda
equinas or the sciatic nerves. Experimental
studies of paralyses in 99
Donaldson, Henry H. A comparison of the
European Norway and albino rats (Mus norvegicus and Mus norvegicus albinus) with
those of North America with respect to the
weight of the central nervous system and to
cranial capacity. 71
Dunn, Elizabeth Hopkins. The influence of
age. sex, weight and relationship upon the
number of niedullated nerve fibers and on the
size of the largest fibers in the ventral root of
the second cervical nerve of the albino rat. 131
FEISS, Henry O. Experimental studies of
paralyses in dogs after mechanical lesions in
their spinal cords, with a note on 'fusion'
attempted in the Cauda equinas or the sciatic
nerves. 99
'Fusion' attempted in the cauda equinas or the
sciatic nerves. Experimental studies of paralyses in dogs after mechanical lesions in their
spinal cords, with a note on 99
GANGLIA and of the spinal nerves. The
structure of the spinal 159
of the embrvo of Rana pipiens. The cerebral 461
of the sheep. On the histology of the cranial autonomic 447
LANDACRE. F. L. The epibranchial placodes
of Lepidosteus osseus and their relation to
the cerebral ganglia. 1
and McLellan, Marie. The cerebral ganglia of the embryo of Rana pipiens. 461
Lepidosteus osseus and their relation to the cerebral ganglia. The epibranchial placodes of 1
McLELLAN, Marie, Landacre, F. L. and.
The cerebral ganglia of the embryo of Rana
pipiens 461
Mitosis in the central nervous system of the albino
rat. The cessation of 547
NECTURUS maculosus (Raf.). The numerical relations of the histological elements in
the retina of 405
Nerve fibers and on the size of the largest fibers in
the ventral root of the second cervical nerve
of the albino rat. The influence of age, sex,
weight and relationship upon the number of
medullated 131
fibers. Degeneration and regeneration of
487
Nerves. Experimental studies of paralyses in
dogs after mechanical lesions in their spinal
cords, with a note on 'fusion' attempted in the
cauda equinas or the sciatic 99
The structure of the spinal ganglia and of
the spinal 159
Nervous system and to cranial capacity. A comparison of the European Norway and albino
rats (Mus norvegicus and Mus norvegicus
albinus) with those of North America with
respect to the weight of the central 71
system of the albino rat. The cessation of
mitosis in the central 547
o
LFACTORY tracts and centers in teleosts.
The 177
rOHNSTOX, .7. B. The telencephalon in cycloI stomes. 341
PARALYSES in dogs after mechanical lesions
in their spinal cords, with a note on 'fusion'
attempted in the cauda equinas or the sciatic
nerves. Experimental studies of 99
Palmer, S.^mcel C. The numerical relations of
the histological elements In the retina of Necturus maculosus (Raf.). 405
Pipiens. The cerebral ganglia of the embryo of
Rana 461
Placodes of Lepidosteus osseus and their relation
to the cerebral ganglia. The epibranchial 1
RANA pipiens. The cerebral ganglia of the
embryo of 461
Ranson, S. VV.vlter. Degeneration and regeneration of nerve fibers. 487
The structure of the spinal ganglia and of
the spinal nerves. 159
Rats (Mus norvegicus and Mus norvegicus albinus)
with those of North America with respect to
the weight of the central nervous system and
to cranial capacity. A comparison of the
European Norway and albino 71
Rat. The cessation of mitosis in the central nervous system of the albino 547
569
570
INDEX
The influence of age, sex, weight and relationship upon the number of meduUated nerve
fibers and on the size of the largest fibers in
the ventral root of the second cervical nerve
of the albino 131
Regeneration of nerve fibers. Degeneration and
487
Retina of Necturus maculosus (Raf.). The numerical relations of the histological elements
in the 405
SEX, weight and relationship upon the number of medullated nerve fibers and on the size
of the largest fibers in the ventral root of the
second cervical nerve of the albino rat. The
influence of age, 131
Sheep. On the histology of the cranial autonomic
ganglia of the 447
Sheldon, Ralph Edward. The olfactory tracts
and centers in teleosts. 177
Spinal cords, with a note on 'fusion' attempted in
the Cauda equinas or the sciatic nerves. Ex
perimental studies of paralyses in dogs after
mechanical lesions in their 99
TELENCEPHALON in cyclostomes. The 341
Teleosts. The olfactory tracts and centers
in 177
VENTRAL root of the second cervical nerve of
the albino rat. The Influence of age, sex,
weight and relationship upon the number
of medullated nerve fibers and on the size of
the largest fibers in the 131
EIGHT and relationship upon the number
of medullated nerve fibers and on the size
of the largest fibers in the ventral root of
the second cervical nerve of the albino rat.
The influence of age, sex, 131
— of the central nervous system and to cranial
capacity. A comparison of the European
Norway and albino rats (Mus norvegicus
and Mus norvegicus albinus) with those of
North America with respect to the 71
